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A STUDY OF PITHINESS IN THE RADISH

THESIS PUB THE DEGREE OF M. S.

Grant B. Snyder
1931

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- Ham-.11-

A Study of Pithiness in the Radish (Raphanus sativus, Linn)

---- Thesis ----

Submitted to the Faculty of the Michigan State
College of Agriculture and Applied
Science in Partial Fulfillment of
the Requirements for the Degree

of Master of Science

Grant B. Snyder

///9 /€/% 3 /
//%,/;;;€?{) "::;2;;Zfififl::A&E#////fi

TH E519

 

Contents

Page
introduction -------------------- 1
Review of literature ----------------- 2
Material and.methods ................. 5
Presentation of data ----------------- 10
Morphological and anatomical considerations - - - lO
Morphological observations --------- 12
Anatomical observations ----------- , 16
Discussion of the relationship between pithi- .
ness and anatomical structure ------ 23
Relationship between pithiness and certain other
phenomena ------------------ 27
Top-root ratio --------------- 27
Specific gravity of root ---------- 43
Correlation in size of top and root ----- 46
Influence of environment on pithiness ------- 48
Environmental observations (methods) ----- 49
Interpretation of ecological data ------ 49
Discussion of environmental effects on growth
and pithiness ------------- 53
Discussion ---------------------- 57
Summary ----------------------- 63
Literature cited ------------------ 65

 

5 Study 2f Pithiness in the Radish (Raphanus sativus, Linn)

Introduction

Pithiness of the radish, a condition of tissue
breakdown within the storage root, has been of long standing

importance to the grower insofar that such roots are coarse,
unpalatable, and of no commercial value as an esculent product.
A radish to be of good quality must be solid, criSp, and
fairly mild in flavor.

The gardener has considered both heredity and factors

of the environment as causal for pithiness although the latter
seems to be most generally designated. Over a period of years
he has noticed that certain varieties and even strains seem to
show pithiness sooner than others and assumed, therefore, that
the condition is hereditary, a matter of poor seed. On the
other hand, he has also observed that the same variety from the
same source, but grown under different environmental conditions

exhibits pithiness in a varied degree. Pithiness seems to be

more prevalent in the hot summer months than in the cooler

periods of spring and fall. Occasionally methods of culture,

the use of large amounts of fertilizer prior to seeding, and
seed below normal in size are thought to either increase or

minimize the percentage of pithiness.

Review of Literature

Available literature does not seem to be very
enlightening as to the actual causes of pithiness. Watts (21)
and Thompson (19) favor the idea that, though the radish is a
cool season plant and does not reapond favorably to a high
temperature, the more important factor is a sufficient supply
of soil moisture. Bailey, (1) (2) on the other hand, con-
siders temperature as the most important factor of the
environment influencing pithiness of the radish. Lloyd (12)
is also of the Opinion that variations of temperature influence
most markedly the quality of the different types of radishes.

There is a distinct difference of Opinion as to the
structure of the radish root. Velenovsky (20) considers the
thickened knob as simply an enlarged hypocotyl. Hegi (9) in
his work concluded that the stem part of the hypocotyl thickens

together with the tap root, building a turnip form, fleshy,

edible knob, or as he called it, 'hypocotyl-knob or gliding

43
stem knob" vhich consists of a single internode. Golinska (7)
is of the opinion that the hypocotyl member plays an essential
part in the origin of the radish knob. Jones and Rosa (10)
state that the portion of the tap root free from laterals is
stem tissue develOped from the .hypocotyl. Sinskaia (18) calls
the enlarged portion a thickened root. Holdenhawer (l4) and
Malinowski (13) consider the swelling of the radish root a
hereditary characteristic, but Sinskaia found that certain
environmental factors, primarily lengthof day, prevented the
formation of a root knob. Johannsen (ll) demonstrated that
various light eXposures exert a greater influence onthe

growth of the root than on that of the shoot. Garner and

Allard (5) describe the radish as a long day plant and that
the shortening of the continuous exposure leads to the ac-
cumulation of carbohydrates inthe plant which checks the
growth length of the t0ps and furthers the building up or
enlargement of the underground part. Each type of growth
corresponds to a definite rate of carbohydrate synthesis and
utilization which may, however, be modified by the environment

and thereby influence the thickening of the root.

- 4

7 Golinska (7) shows that the radish has two periods of
deve10pment, the first in which the thickening of the root takes
place and in which the accumulated products of assimilation
are stored, and the second in which the flower shoot is pro-
duced at the expense of the accumulated storage products in
the root.

Riolle (17) found practically no starch in the various
varieties of Japanese and French radishes studied and where
it was found it was located in the epidermis in minute quantities.
He found, however, that considerable sugar was stored in the
root. Conrad (3) found that protopectin and pectin made up

26.87 per cent and pectic acid 15.37 per cent of the dry weight

of the root.

This review does not seem to yield any general agree-
ment as to the possible factors reaponsible for pithiness or.
what actually occurs within the root when such tissue breakdown
takes place, other than, perhaps, the effect of environment
on growth of the plant. If, therefore, such environmental
factors as temperature, moisture, and light seem to be possible
causes for the condition there should be certain physiological

reactions which influence, directly or indirectly, the anatom-

ical changes within the root to cause pithiness.

Materials and Methods

 

The common radish‘ Raphanus sativus) because of its
antiquity and almost universal culture, contains many diver-
sified forms as to shape, size, color of root, and season of

maturity. The botanical characteristics are, however, the same

for the various sorts.

_ It has been noticed by casual observation that the
length of time required to reach edible maturity and quickness
of tissue breakdown show a slight relationship. Radishes of
a globular shape seem to show pithiness more readily than do
those sorts which are elongated. In order to include these

ideas in the studies the following varieties were chosen as
representative sorts. I

1. French Breakfast, seed to edible stage 3 - 4
weeks, growth very rapid, root oval in shape, tap very small.
The variety is used very largely for forcing under glass and
as an early Spring and late fall sort out-of—doors. It becomes
pithy very readily.

2. Scarlet Globe, seed to edible stage 4 weeks,
growth rapid, root oblate to globular in shape, tap small.
This variety is grown under glass and out-of—doors as a spring

and fall months sort. Though its growth is somewhat similar

to French Breakfast, the roots remain free from pithiness
longer after reaching an edible size.)

3. White Icicle, seed to edible stage 4 - 6 weeks,
growth semi-rapid, root elongated and cylindrical, t0p medium
large. This variety is grown as a spring and fall sort and to

a small extent for forcing. It becomes pithy comparatively

slowly.

4. Giant Stuttgart, seed to edible stage 6 - 8 weeks,
growth slow, root tankard cylindrical in shape, tOp large. It
is planted as a summer and fall sort and becomes pithy very
slowly.

5. Black Spanish, seed to edible stage 10 - 12
weeks, root very large, elongated and cylindrical, top very
large. It is used only as a late fall and winter sort and
seldom shows very great percentage of tissue breakdown.

Seed of each of the varieties studied was planted at
East Lansing, Michigan, on May 28, June 30, and July 18, 1928,
in a soil ranging from a light to a heavy loam underlaid at
a two-foot depth with sand. The May planting was used for

anatomical studies while the June and July plantings were

used for both anatomical and ecological observations.

The plantings at Amherst, Massachusetts, were made on
September 9, 1929, in a medium loam soil. One-half of the plot
was mulched with a heavy grade of commercial mulch paper.

Both anatomical and ec010gical studies were made with the
plants on the mulched and unmulched areas.

Approximately every two days from each of the plant-
ings random samples of 50 plants were carefully pulled. These
were taken to the laboratory, washed with fresh water, and then
dried until no free water remained on the leaves or roots.

The top was cut from the root at the base of the cotyledon
leaves and both parts weighed. The roots were further placed,
individually, in a graduated cylinder filled to a given point
with dietilled water and the diaplacement noted. From the
displacement over the weight of the root the Specific gravity
was calculated for the individual.

Each root was cut at three points and the-apparent
pithiness noted. Pithiness of the radish root as stated was
an approximation of the visible percentage of tissue breakdown.
Such breakdown was not uniform or restricted to one section.

It occurred most frequently on small areas scattered through

the parenchyma tissue at the wider diameter portions of the root.

- 8

This was especially true of the initial stages. The advanced
stages could be quite accurately noted because the pithy areas
were well defined and outlined. Therefore, there may have

been some error in approximating the degreeof pithiness and in
classifying the individual into its proper class by the method

used. On the other hand, the graduations were wide enough to
allow for placements of sufficient accuracy for correlation

of the factors involved.

The arbitrary groupings set up as standards of com-
parison (see Plate I) were as follows: trace 0 i lO,one
10 - 20, two 20 ~ 40, three 40 - 60, four 60 i 80, five 80 -
100 per cent of tissue breakdown.

Pithiness in the first two groups was not sufficient
to seriously impair the edible quality of the roots. Group
three was of little value and four and five were unpalatable.
Therefore, groups three, four, and five, eSpecially the latter
two, are in all cases of interpretation considered undesirable
for commercial use.

As each lot was examined sections were set aside for
anatomical study. Common histological technique was used, the

sections being stained with safranin and Delafield's haematoxalin.

-9

Plate I

Stages OF Pithiness

'Tfeoce 040% I |O-2.0/

   

A

y

       

 

 

- 10

In the mathematical data presented the geometric
mean was used in preference to the arithematic mean because
'of its greater reliability. The coefficient of correlation

was calculated on the following basis, r. and the

._IL—
{I 4"

probable error of r by the formula that Per. 4:13., 0.6745.
. . yrfi-’ .

No difference less than three times its probable error was
considered significant. Crist and Stout's (4) interpre-
tation of the significance of the coefficient of correlation
was used on the following basis: (a) If ”r” is 0.5 (plus
or minus) or greater, correlation is practically certain.
(b) In order to be reliable ”r'must be at least four times
its probable error. (c) If, under various conditions of
experimentation, ”r” persists in having the same sign,
though not always in itself significant, there is some

evidence of a general though weak relationship of the

character of this sign between the two variables.
Presentation 22 Data

MorphOIOgical and Anatomical Considerations

The actual condition of pithiness is in itself

strictly anatomical in that it is a breakdown of tissue

- 11

within the storage portion of the radish root. Therefore to
intelligently relate cause and effect it is essential to.
include a brief consideration of the grosser morpholOgical
and anatomical observations made during the progress of the
studies on pithiness.

While considerable difference of Opinion exists as
to whether the storage portion of the radish is definitely
a rest, a hypocotyl, or part root and part hypocotyl, the
general deduction from the works of Gerard (6), Haberlandt
(8), Velenovsky (20), and Golinska (7) seems to be that the
hypocotyl or transition region between the root and the t0p
is very indefinitely defined and variable in its limits.
The structure of the root does not abruptly chahge into that
of the stem but merges gradually so that very frequently it
is difficult to actually locate the transition zone. The
point of disputain the case of the radish seems to be to
definitely locate the region of morpholOgical and anatomical
change from root to stem.

Most authorities agree that the storage portion

has practically the same anatomical structure as the tap
root, and yet, on the upper side of the enlarged root of

certain varieties Golinska (7) found no root hairs, a lightly

412
cutinized outer wall, the appearance of a few stomata, and
anthocyanin in certain cells of the pericycle and cortex.
However, since the principal mark of root construction --
the arrangement of the conducting tissues andthe centripetal
development of the protoxylem strands -- is preserved in the
storage region, that portion of the plant below the base of
the cotyledon leaves or the crown of the enlarged part of

the tap root, is designated as root in this paper.

Morphological Observations
Though the several varieties studied were more or
less variable as to size,
shape, color, and time
of maturity, all ex-
hibited the same char-

acteristics in their

morphological develop-
ment.

The radish
seed on germinating
produces a radicle

which elongates into a

 

cylindrical structure
Illustration 1. Showing the elongated
zone between the storage region of the
root and the base of the cotyledon
leaves. A spindly plant.

- 13

or primary root. This, on becoming established in the soil,
lengthens rapidly, especially the zone between the region of
root hair development and the base of the cotyledon leaves.
This is the zone commonly known as hypocotyl but is here
designated as root. The elongation of this portion of the
root is regulated, markedly, by the environment, in that
high temperature and short light exposure tends to cause an
excessive deve10pment of its longitudinal axis or what is
more commonly known as a spindly or leggy plant. (Illus-
tration 1). The storage portion is initiated in this section
of the root and usually at its lower extremity, with the
result that where the zone was abnOrmally long a constricted
region or neck was apparent between the enlarged part and
the base of the cotyledon leaves.

As soon as the leaves started to function to the
extent that carbohydrates were synthesized in excess of

that needed for actual growth, the surplus was apparently

translocated to the storage region of the root with the re-

sult that the inner tissue, the root prOper, increased in

size more rapidly than the outer protective tissue. This

caused two opposite
longitudinal fissures
to develOp, opposite
to the axis of the
cotyledon leaves,
thus dividing the
outer protective
tissue into two equal
parts. As theroot
enlarged and separ-

ated these coverings,

they became more or

less detached from the

root pr0per and took on

- l4

 

Illustration 2. Showing the longi-
tudinal split of the primary
cortex to form two flaps, below
which the storage portion of the
true root enlarges.

the appearance of two pale flaps, apparently growing out of

the hypocotyl just below the cotyledon leaves (Illustration 2).

These flaps persisted for varying periods of time, usually

until the storage stage of the root was well advanced, before

disintegrating.

The storage region of the root increased in size, ap-

parently, from a central axis in both longitudinal and vertical

planes.

The secondary or lateral roots develOp primarily
from the taproot and varying portions of the storage root
from two shallow grooves which run longitudinally in line
with the cotyledon leaves. These lateral roots generally
develOp onthe lower half of the enlarged storage region
in the case of the quick-growing globular varieties.. Many
instances, however, were noted in the Amherst plots where
lateral roots were deve10ped well up to the crown. The
larger elongated sorts developed such roots quite consis-
tently well up to the crown of the storage region.

In the East Lansing plots the varieties French

Breakfast and Scarlet Globe fre-

quently produced secondary swell- /‘

, .., , \
ings of the tap root. (Illus- / 0‘s

/ \

tration 3). These swellings . \)
varied in number for the individual /Q
plant from one to five, usually one ’l,‘F \>
to three, and beds similar ap- /’/ \\
pearance to the normal storage / £3
region except that they were white I , u
and produced lateral roots along Illustration 3. Showing

secondary swellings of a
their entire longitudinal axis. Scarlet Globe radish root

- 16

This condition was apparently an attempt to produce a storage
region lower down on the axis of the root where the soil
temperature was lower than in the top one or two inches of
soil. Such secondary swellings were not noticed on the
other varieties under observation.

These morph010gica1 observations are similar to,

and in the main bear out, those reported by Golinska (7).

Anatomical Observations

The following observations present only such
anatomical structure as is actually associated, directly
or indirectly, with the condition of pithiness of the

storage portion of the root.
A cross-section of a young radish root a few days

old exhibits two distinct groups of tissue, the central

cylinder and its outer protective tissue, the primary cortex.

(Plate III A: VI A). The primary cortex is approximately

six times as broad as the central cylinder. It has around
its outer side a single layer of roundish thin walled cells,

the epidermis; on its inner circumference a single layer of

somewhat elongated to square cells strengthened by CaSparian

- 17

strips, the endodermis and between the epidermis and endo-
dermis, large thin walled parenchyma cells. (Plate VI A).
The tissue of the primary cortex does not divide, and it
enlarges but very little and consequently must burst on the
enlargement in diameter of the central cylinder as noted
under morphological observations (page 12).

The central cylinder (Plate VI A: X A) is bounded
on its outerside, in immediate proximity to the endodermis,
by the pericycle, which is composed primarily of a single
row of cells, but because of rapid division may frequently
appear as two- or three-celled in thickness. Immediately
inside the pericycle, and originating from it at two 0p-
posite points, is the primary xylem. This progresses centri-
petally until a strand is built which proceeds in the plane
of the cotyledons. Opposite to this plane, and also arising

from the pericycle, are located the two groups of primary

phloem elements which are separated from the primary xylem

by small parenchyma cells. Some of these parenchyma cells

divide and give rise to the procambium which lies between

the protoxylem and protOphloem.

- 18

This procambium later initiates (Plates VIII 3, X A)
new tissue and thus forms a cambium ring by which the xylem
part of the central cylinder is surrounded. The initial
supporting and mechanical tissues also become apparent at
about this stage of development.

As soon as the central cylinder enlarges in diameter
to a point at which the primary cortex is split, the pericycle
forms on its outer periphery secondary cortex and periderm
tissue (Plate X, A) and the cambium initiates, on its outer
side, secondary phloem with its accompanying mechanical tissue
and on its inner side secondary xylem and supporting elements
plus parenchyma or storage tissue.

In this manner the structure of the mature storage
region of the radish is initiated.

The study of a cross-section of a mature root shows
(1) a periderm varying in thickness from one to four layers
of small, compact, thick walled cells which in some cases,
especially the winter varieties such as Black Spanish, are
highly lignified and even corky in character. (2) A cortical

region which is comparatively narrow in relation to the di-

ameter of the whole and in which the concentric and irre-

gularly arranged cells are small, compact, thin walled and

- l9

parenchymatous in type. The cortical region of the quick
growing sorts, Scarlet Globe, (Plate III G) is considerably
narrower and the cortical parenchyma cells much larger than
in the slow growing sorts, Black Spanish (Plate V D). In
general, these cortical cells do not increase materially in
number after their initial formation, although they may in-
crease somewhat in size (Plate III C, compare with G). In
the colored varieties the color pigment, anthocyanin, is
located in the outer part of the cortex and possibly in the
periderm. (3) The cambium ring (Plates III G, v 0, IX A)
which marks the boundary between the cortex and phloem and

is composed of merristematic tissue inside of which are

grouped the vascular elements with their supporting tissue.
(4) The xylem parenchyma, which lies between the cambium
ring and the primary xylem (Plate IX A), and, since it is
the storage region, composes the largest percentage of the
tissue of the storage root. Arranged in a radial plane
throughout this region are varying numbers of vascular rays
composed of varying numbers of vascular elements in which
the tracheids are outstandingly prominent and large, and in
which, in some cases, phloem elements seem to be present

(Plates III c to c, IV A, and D, v D, IX A, K: A).

The parenchyma cells are thin walled and vary in size from
small in immediate proximity to the cambium ring, vascular
elements, and primary xylem, to very large intermediate to
these elements. (Plates IX A and B, XI A and B). Therefore

the greater the amount of vascular and supporting tissue

within the secondary xylem, the higher the proportion of small

to large parenchyma cells. (5) The stele in which are
located the primary conducting elements, the primary xylem
plus its supporting tissue (Plates Iv A and B, IX A, x: A).
Though the character of this varies considerably the primary
xylem most generally appears as a definite or slightly
modified four-armed star.

The general anatomical observations as outlined for
the seedling and mature storage root are basic in character
for all the varieties studied, as is also the development of
the root from the primary elements to the mature structure.
However, each variety and more eSpecially each type, as
spring, summer, and winter, exhibits distinct modifications
from these basic characteristics, in size and arrangement.
of cells and in percentage of kind of tissue in relation

to the whole, and which are peculiar only to that variety

or type.

- 21

The quick growing varieties, French Breakfast and
Scarlet Globe as the extreme examples observed (Plates III
E, F, G; v 0) exhibited: a thin periderm which at times
was lightly lignified, a narrow cortical region, a cambium
ring in which the vascular elements were Spaced comparative-
ly far apart, a xylem parenchyma composed of large irre-
gularly arranged cells, few vascular rays which were very
sparsely supplied with vascular elements and a stele of
prominent conducting elements. The slower growing varie-
ties, Black Spanish (Plate V D) taken as the extreme
observed, on the other hand, exhibited: a thick periderm

in which the outer cells were distinctly corky, a thick
cortical region composed of very small cells, a very dis-

tinct cambium ring in which the vascular elements were spaced
very close tOgether, a xylem parenchyma composed of small
cells arranged in quite definite radial rows, many vascular
rays in which the elements were quite closely Spaced, and

a stele in which the primary elements were not outstandingly
prominent. The other varieties studied graduated toward
either one of these extremes according to their rapidity of

development.

- 22

The quick growing sorts deveIOped secondary tissue
more rapidly than the slower growing sorts which is of im-
portance because the more rapid the develOpment of the xylem
parenchyma the less supporting tissue is usually evident.

This generally results in increasing the size of the cells

composing the xylem parenchyma.

The quicker the deveIOpment of the storage root the
narrower the cortical region and the largerthe cells of the
cortex. Environment, however, may affect this observation

because in the case of the East Lansing plantings where the

soil was hot and dry, the three early maturing sorts fre-

quently exhibited an abnormally thickened cortex. Such a
condition was never observed in the Amherst plantings.

From an observational point of view it appeared as
though the tracheids were larger and more heavily lignified
in the East Lansing plantings than in the Amherst plantings.
Such a condition might lOgically be expected where the roots
develoPed in a soil with a low moisture content.

Though the anatomical studies as reported are pre-

liminary in character and consider only the grosser and more

basic background in the structure of the radish storage root,

- 23

they are sufficient for the problem under consideration to
warrant the conclusion of a definite variation of the in-
dividual in relation to the rapidity of its deveIOpment and
growth. Further, as will be explained later in this paper,
tissue breakdown or pithiness develops more readily and
progresses more rapidly as the structure of the storage

region deviates toward the one extreme.

Discussion on the Relationship of Pithiness

and Anatomical Structure

Pithiness in the radish root develops only in the
xylem parenchyma tissue, and is invariably initiated and

first apparent in the oldest and most mature zone. This
zone, while variable to a greater or lesser degree, generally
was located just below the horizontal plane of the shoulders
of the storage region or at its approximate widest diameter.
Traces of tissue breakdown usually were noted between the
cambium ring)stele and vascular rays, or at the points most
remote from the conducting and supporting tissue. (Plates

IV A, B; V A, B, C). As the percentage of pithiness in-

- 24

creased, areas at various points’usually below the initial
point, broke down, and with their increase in number and
size fused into a smaller number of larger hollow areas.
These in turn progressed in the same manner until, in a

root designated as 100 per cent pithy, only the primary con-
ducting tissue of the stele, a few of the tertiary xylem
strands and a small percentage of the parenchyma cellsin
immediate proximity to the cambium ring and secondary xylem
strands remainedbesides, of course, the cortex and periderm
which never broke down. In extreme instances all tissue
inside of the cambium ring, from crown to tap root, broke
down. It is important to note that in the pregress of
pithiness from its initial stage onward the large parenchyma

cells farthest removed from supporting and conducting tissue

were first and the smaller parenchyma cells around the
vascular elements last, to break down. Therefore, the
larger the cells within the xylem parenchyma and the fewer
the conducting and supporting elements the more readily the
tissues break down and the more rapid the deveIOpment of

pithiness.

- 25

French Breakfast with its characteristically large
cells within the xylem parenchyma and small amount of vascular
elements was invariably the first of the varieties studied
to break down. Scarlet Globe with a similar size of cell but
having generally more vascular tissue held up slightly longer.
The other varieties followed in order: White Icicle, Giant
Stuttgart, and Black Spanish. The latter two varieties
with small cells and a large amount of vascular tissue ex-
hibited pithiness or tissue breakdown very tardily.

The initial stages of pithiness appeared quite
definitely to be a severing or tearing apart of two or three
cells because their walls did not appear shrunken and no in-
dication of a plasmolytic condition was apparent. This was
true also where fair sized areas were pithy. In Plate IX C
a typical initial stage of pithiness is shown; A, two cells
just about ready to sever; B, two cells whose connecting
wall has ruptured; and C, where the tissue of a large
number of cells has broken down to form a pithy area. No
indication of collapsed tissue was apparent until 60 per cent
or more breakdown was noted and even then, in many cases,

there was little evidence of such a condition (Plate V B).

- 26

The largest cells were always the first to break
down and it appeared as though these cells, on reaching their
maximum size, were incapable of taking care of any further
increased pressure from within with the result of a rupture
of the cell wall. Small cells, such as found in immediate

proximity to the supporting and conducting tissue, were able

to withstand such increased volume and consequently did not
rupture until all the larger cells surrounding them had

broken down.

At this time it is not possible to state what be-
comes of the cellular material after tissue breakdown has
taken place. In extreme cases of pithiness only about 10
per cent of the original cells of the xylem parenchyma re-
mained, and yet there were no cellremnants apparent in the
sections examined to support the assumption that the tissue
disintegrates. Also very little shrunken tissue was noticed.

In the many sections examined there was no indication
of a thickening of the cell wall in any of the xylem paren-
chyma tissue due to or associated with pithiness. In many

cases, however, there were found groups of very small cells

which were comparatively thick walled, which formed around a

- 27

xylem or vascular strand. (Plate IX 3). Roots showing cells
of this type were invariably pithy and of coarse texture.

The older the root, regardless of whether pithiness was ap-
parent to any marked degree, the more pronounced was the-
lignification of the primary xylem, the tracheids of the
vascular rays and the phloem and xylem tissue of the cambium
ring. (Plates V C, VI B). Lignified tissue was in all

cases associated with a root that was coarse and tough and of

poor quality.

Relation Between Pithiness and Certain Other Phenomena

Top-Root Ratio

Because pithiness frequently deveIOps just prior to

seed stalk formation, at which time increased tranSpiration
or a withdrawal of carbohydrates may be evident to support

such growth, a precise study of the relationship between
t0p, root, and pithiness seemed to demand careful consider-
ation.

Experimental evidence such as obtained by Crist
and Stout (4), Weaver (23), and Pearsall (15, 16) leads to

the conclusion that herbaceous plants exhibit a rather de-

- 28

finite and positive correlation of top to root for a given

variety grown in a uniform environment. This does not mean
that the plants are absolute or fixed in a given pr0portion
of top to root, but that as one part increases in size and

weight the othervaries pr0portionately.

In noting the growth of the radish from seed to
seed a definite relationship of tOp to root was observed.

The ratio varied from less than one to more than one, but
nevertheless as one part, the top, increased in size and green
weight, the other part, the root, increased to a greater or
lesser degree correSpondingly.

This particular plant exhibits three definite ratios
of top to root during its entire growing period (Plate II and
Chart II). These periods, the writer has designated as (l)
establishment, high top root ratio or a rapid top growth of
cotyledon and first true leaves and a slow root growth; (2)
food elaboration and storage, lower t0p root ratio or a
slowing up of top growth with a marked increase of root size
and weight, eSpecially of the storage portion; (3) maturity

and seed formation, high tOp root ratio or a very rapid

growth of t0p in the production of the seed stalk and a de-
cided slowing up of the root increase. This may be shown

graphically in the following manner:

-29

plate H
Establ isbmenh

    
    

 

 

 

 

 

 

 

 

 

 

 

 

Seed $to|k Formal IOI’)

“MAMA

   

 

- 30

 

 

 
 
  

JET Adcrfuxity
cuwd

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Food ECO bom‘h‘on
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These three periods are not fixed with reSpect to

their durations of time.

The quick growing, small rooted sorts such as French
Breakfast and Scarlet Globe, under Optimum conditions of
environment exhibit comparatively short periods of establish-
ment and storage whereas the slower growing larger rooted
White Icicle shows a slightly longer time factor for the two

stages. The large rooted late varieties, Black Spanish and

Giant Stuttgart, exhibit still longer preportionate periods

of establishment and storage.

The third stage, maturity, while no detailed ob-
servations are presented, tends to be more uniform in time
for all varieties from the observations made.

Of particular interest is the fact that pithiness
wasvery seldom apparent during the first stage of develop-
ment, namely establishment. However, as the storage stage
develOped pithiness became more and more noticeable and by
the time maturity and seed develoPment was reached almost
every root showed complete breakdown of the storage area.

Tables 1 - 10 show that in every case pithiness
increased as the tOp-root ratio decreased. As long as the
tOp (green weight) was greater than the root (green weight)
or above one, there was relatively no pithiness. Appro-
ximately at the time top and root reached equality pithiness
became apparent and as soon as this point was passed and the
tOp-root ratio became less than one, cell breakdown increased
to a greater or lesser degree until the maturity stage when
practically no parenchyma tissue remained within the root.

While the first stages of pithiness were noticeable at the

approximate period of equality in weight of t0p and weight of

root, no cases except in Tables III and IV, which may have

been due to error in proper classification, were observed

-32

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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-34

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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-35

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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-36

 

 

 

 

 

 

 

 

 

 

 

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-38

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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-39

where the pithy areascomposed 40 per cent or more of the whole
prior to or at this stage of deve10pment. Pithiness of a
degree (40 per cent or more) to prevent the commercial use of
the roots deveIOped only at varying periods of time after
equality of the top and root had been passed.

In comparing the data in Tables 1 - 10 with their
graphic presentation on Chart I, it is apparent that the re-
lationship in each group of t0p over root and pithiness falls
in a rather definite class interval even though different
varieties planted at different times in the growing period were
considered. The relationship was even closer than shown,
because in the case of Scarlet Globe 7/18, French Breakfast
7/18, and White Icicle 6/30 and 7/18, where the line T/R
crosses P below the point of 1.50, pithiness was confined to
mere traces. Even so, the curve of relationship is significant
as shown.

Vhen the weights of the tOp, root, and the top-root
ratio were plotted against pithiness for different varieties

* ‘
planted in varied environments their relationships were quite
uniform. (Chart II). Regardless of environment or time
elapsed from seeding, pithiness was noticed first at approx-

imately the equality point of tap and root weight. As their

~40

 

 

 

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'42

weights increased and their ratios decreased, cell breakdown
increased. In both the midsummer plantings of French Breakfast
and White Icicle, the entire growth period was comparatively

rapid. The initial top-root ratio started high but fell

rapidly to the equality point of one and beyond even though
the lines of growth of tOp and root did not vary widely in
their ascent. In these cases pithiness was noticed just
prior to equality, but increased very rapidly after this

point had been passed.

In the fall plantings of the same varieties, the
growth lines for the entire period were more gradual in their
ascent and although the t0p and root exhibited the same trend
a wider divergence in their growth was apparent than in the
earlier plantings. The tOp-root ratio started comparatively
low and fell gradually to the equality point and beyond to
its lowest level. Pithiness did not become apparent until
the tOp and root were near or at equality. Beyond this point,
while the percentage increase was quite rapid, the areas were

small and did not seriously influence the palatability of

the roots.

The point of interest is that although pithiness

was noticeable at approximately the point of equality of top

and root, in all cases the late plantings with a more gradual

- 43

tOp over root decrease took longer in developing 40 per cent
or more pithiness per root. In the earlier plantings the
tap and root growth increased very rapidly during the entire
period of observation while the late plantings exhibited a
slower growth with a noticeable decrease shortly after equality
had been passed. After equality of root and top had been
reached and passed so that a low ratio prevailed, rapidity
of growth during the storage period tended toward rapidity
of tissue breakdown, while a slower growth of more or less
uniform prOportions of t0p and root tended to reduce pithi-
ness, eSpecially of the degree which prevents the use of the

roots for dammercial purposes.

Specific Gravity of Root

Specific gravity was determined as a rough check
on the observer's estimates of pithiness. This is, of course,

open to the objection that tissue, while still intact, may
vary greatly in cell contents, and that errors in determin-
ation of volume may be unduly large in small roots. In fact,
both of these defects were encountered in the course of this

work, the first being particularly apparent in samples gathered

’44

immediately before and shortly after a rain, and the second
is marked in the first one or two lots in Tables I, II, III,

and V. Nevertheless, the relationships exhibited seem to

justify presentation of the results.

In general, Specific gravity in the young roots was
about one. The appearance of pithiness coincided with a de-
crease in Specific gravity and as pithiness increased, Specific

gravity decreased. The point is emphasized, however, that
pithiness increases more rapidly than specific gravity de-
creases. By definition, as specific gravity decreases, the
ratio of volume to weight increases. Analysis of the figures
used in computing specific gravity (Chart III) shows that the
ratio increase is not due to increase in weight increment
(which is actually most rapid at this time), but to a still

more rapid increase in volume.

In view of the rather general Opinion that rapid

growth causes pithiness it is of interest to note the slight

relationship which seems to exist between Specific gravity,

top-root ratio, and pithiness as shown in Tables II, IV, and

V. A high top-root ratio shows a tendency toward a cor-

reSpondingly high Specific gravity and little or no pithiness.

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'46

It would seem in comparing Tables II, IV, and VI with I, III,
and V, that a very rapid growth of t0p and root results in
a correSpondingly higher specific gravity than where a

slower growth of t0p and root was apparent.

Correlation in Size of TOp and Root

Assuming that tranSpiration and carbohydrate
exhaustion of the root are, at least in some degree, pro-
portional to increase in the top, flattening of the tap-
root ratio curve (A) should be accompanied by a similar
flattening of the curve of pithiness (as at B) and a

rather high negative correlation should exist. Actually

pithiness increases most rapidly while the top-root

ratio is changing least. Consequently it is not surpris-
ing that there is no correlation of the taperoot ratio,
under the conditions of these trials, with the degree d?

pithiness.

-4'7

 

'40
1: Pithiness C -

 

 

 

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There is, however, a marked positive correlation
between size of t0p and size of root, the importance of which
will appear in the discussion. (Tables 1 - 10). While the
coefficient of correlation was variable for the given lots
and showed no definite relation of one with another as to
magnitude, they were all positive in character. In the 97
lots shown 58.6 per cent of them had a coefficient of cor-
relation of .5 or more, and in 79.6 per cent of all the
cases ”r” was at least four times its probable error. Where
the categories of each lot were grouped all exhibited in-
dividually a highly significant coefficient of correlation

which was decidedly greater than four times its probable

.error, the most significant being (Table III) 0.910 t

0.005, and the least significant (Table IV) .509 z .024.

- 48

This correlation, it is emphasized, is no greater
in the varieties which do not develop extensive pithiness

than it is in those which do.

Influence of Environment on Pithiness

Assuming that certain physiological phenomena, as
transpiration, carbohydrate utilization, and growth tension,
are individually or in their associations one with another
causal factors of pithiness, it is rec0gnized that they are
controlled, to a greater or lesser degree, by the conditions
of the plant's environment. The environment is antecedent
to the actual reaction or condition within the structure of
the plant causing tissue breakdown or pithiness.

While all the factors of environment, in all prob-
ability, are influential in plant growth, certain specific
ones are more so than others. The factors considered of
major importance for the studies under consideration were
climatic -- temperature, light, and precipitation! and .
edaphic -- temperature and moisture. It is realized, however,

that other ecolOgical factors such as wind and humidity also

have some effect and must be considered in the final analysis

after a hypothesis is somewhat definitely established.

-49

Environmental Observations (Methods)

Weaver (22) found that the major portion of the
fibrous root system of the radish was located in the t0p 18
inches of the soil, and, therefore, in determining soil
moisture for the present studies this was the area con-
sidered. Determinations were made at 0 N 6, 6 - 12, 12 - 18
inches depth in at least three different locations in each
plot and the mean of each used in the presented data.

(Chart Iv).

A recording soil thermOgraph with the cable located
six inches below the surface was used in obtaining the soil
temperature. The mean daily temperature is plotted on Chart IV.

The data for atmospheric temperature, precipitation,
and sunlight were obtained from the weather stations at East
Lansing and Amherst, both of which were near enough to the
plots so that no sufficient difference of the factors was

found to cause error in interpretation. (Chart V).

Interpretation of Ec010gical Data

To interpret the data presented (Charts IV, V) in

such a manner as to stress one factor as outstanding in its

ll... fiQ—p’ v

I
I
,
I
i
A
I
4

 

 

-51

 

'52

influence on pithiness is not possible in the work reported

at this time. Trends, however, are apparent and indicate a

course for more detailed and better controlled research.
Ecological observations of the three plots in which

the various varieties were grown are of the following nature:

East Lansing: Soil temperature relatively high, 750 F. uni-

 

form; soil moisture low, 10 - 11 per cent, uniform, except
for the later part of July due to slight rainfall; air
temperature, high day and cool night with 7d3 F. mean;
precipitation low, 2.7 inches, and well distributed; sun-
light 80 per cent possible.

Amherst unmulched areas Soil temperature, high initial, _

 

V5

750 F. but gradually decreasing to a low point of 50 - 55° r.
at the end of the period; soil moisture, high, 21.5 per cent,
fluctuating widely but uniformly for the three depths noted;
air temperature, a high day with cool night (mean 65° F.)
during the first part of September and cool day and cold
night (mean 45° F.) during the first part of October; pre-
cipitation, normal 5.04 inches, received largely in three

periods; sunlight low, 55 per cent possible and comparatively

short days.

Amherst, mulched area: The factors of environment were the
same as noted for the unmulched area except that the soil
temperature was quite uniformly 2 - 6° F. higher and the soil
moisture, while slightly lower in mean percentages (20.7),

was very much less variable.

It is of interest to note that with the dry soil
at East Lansing precipitation mast markedly influenced soil
temperature (Chart IV, July 18 - 28), while at Amherst, with
a relatively high soil moisture, air temperature and sunlight
were the factors causing fluctuations of soil temperature

(Chart IV, Sept. 23 - 30, Oct. 4 - 8).

Discussion of Environmental Effects on Growth and Pithiness

In comparing the weather data with that for the
growth (Charts II, IV, V) and development of pithiness a
rather definite relationship is noticed. The July 18 plant-
ings exhibited a rapid growth from the time of germination
until maturity. Tissue breakdown was correSpondingly rapid
from the time of t0p root equality to maturity. Similar

growth behavior and tissue breakdown was noted for the June

30 planting except that the initial stages developed at a

- 54

slower rate. For the September 9 plantings, unmulched area,
growth and subsequent pithiness was very slow and gradual.

On the mulched area growth was somewhat more rapid, especially
during the establishment stage, and pithiness more pronounced.

Precipitation influenced specific gravity of the
roots, eSpecially when the first stages of pithiness were
apparent, as stated on page 43.

This fact might justify the commercial practice of
watering just prior to pulling, especially if the soil was
dry, to increase the water content of the root and, therefore,
the quality even though pithiness up to 40 per cent is
evident.

Where other factors are equal, either temperature
or moisture may be the limiting condition in growth and
pithiness. In the June 30 plantings a slight increase in
soil moisture influenced the plant character in comparison
to the July 18 plantings while in the mulched area of the
September 9 plantings a slight increase in temperature over
the unmulched area increased rapidity of growth and tissue

breakdown. The indications are that there is an Optimum

degree of temperature and soil moisture at which radishes

- 55

maintain a proper balance of tOp and root growth, and, therefore,

a slower tendency to show pithiness. These factors which in

general are applicable to the whole may vary slightly for the
individual variety and even strains of such varieties.

The radish is a long day plant, according to Garner
and Allard (5), and thus light limits very sharply the growth
of the plant and, since the growth ratio of t0p and root ine
fluences pithiness, has a direct bearing on pithiness. There-
fore, another explanation of the behavior of the plants in the
September 9 planting may be related to photoperiodism insofar
that food elaboration and carbohydrate storage took place
rather than the exhaustion of such material in seed stalk and
seed production. The June 30 and July 18 plantings with long
light exposures exhibited just the reversed conditions in
that carbohydrate exhaustion and tissue breakdown were pre-
dominant over food elaboration and storage within the root.

A high soil moisture and a low temperature (air and
therefore soil) combined with a short light exposure produced
a slow t0p and root growth and delayed pithiness. A low soil
moisture with a high temperature (air and therefore soil)
combined with a long light exposure produced a rapid tap and

root growth with a subsequent quick breakdown of root tissue.

’56

A high temperature (air and soil) and a low moisture
combined with short light exposure produced a high initial

tap root ratio but a very rapid fall to equilibrium and beyond.
A low temperature (air and soil) and a high soil moisture com-

bined with a long light exposure produced a low initial tOp-
root ratio and a more gradual fall to the point of equilibrium
and beyond.

In brief, though air temperature, soil temperature,
soil moisture, and length of light exposure, and possibly
other factors, each plays a definite role, to none can a
dominant role be assigned. The Optimum soil moisture un-
doubtedly varies with the temperature and vice versa. Con-
sequently the radish plant at any stage of its development
is the summation of several variables, few of which may

be varied without changing the other factors. Absolute

separation of these factors on material grown other than

under closely controlled conditions is impossible.
Nevertheless, the present study seems to warrant

the tentative conclusion as a basis for further study under

controlled conditions, that for climatic and soil conditions
such as prevail at East Lansing and at Amherst, air temper-
ature is the most important single factor governing pithi-
ness in radishes.
Discussion

The study of pithiness shows a very close relation-
ship between the environmental factors, temperature, moisture
and light exposure, and the rapidity of growth and deve10pment
of the top and root of the radish. These, in turn, influence
the rate of the physiological processes of the plant in
such a manner as to accelerate or retard tissue breakdown in
the root. Anatomical structure of the root influences pithi-
ness indirectly. Roots having large storage cells and little
conducting and supporting tissue are most readily affected
by the physiological processes which cause tissue breakdown.

Pithiness is the effect of one or more physiologi-
cal factors which cause a strain or tension within the xylem
parenchyma resulting in a rupture or breakdown of the tissue
within this region of the storage root. Such a breakdown
was always first apparent at the approximate time (1) of

equality of top and root weight, (2) of equality of volume

-58

of root and weight (mass) of root and (3) when the specific
gravity equalled one. This was true regardless of the variety
or environment. Environmental influence was more pronounced
after the above three conditions had been met..

Even though the percentage of pithiness increased
as the ratio of top to root decreased, growth of both these
parts increased at a variable rate during the entire period
of development of the plant. If the physiological processes,
such as the withdrawal of water from the root by excessive
transpiration or the withdrawal of reserve carbohydrates to
promote top growth, are destructive in character, root
growth should not take place, especially after pithiness has
become apparent to the extent of 60 percent. or more.

When the rate of water loss, by transpiration, is
greater than the rate of absorption, the plant will draw
on the reserve water supply within the storage root. This
may cause plasmalysis and ultimately a collapse of the
tissue or pithiness. Thus, if pithiness is the result of
such a breakdown of the tissues, anatomical examinations
should reveal shrunken or collapsed cells. The observa-
tions made exhibited very little tissue breakdown of this

kind but rather the cells surrounding the pithy areas

-59

had the distinct appearance of having been torn apart.

Ehysiologically, excess transpiration should cause
a marked slowing up of plant growth. Such a checking of
growth, however, was never apparent in any of the observations
made. Even so, excess transpiration might account for pithi-
ness through its influence on other physiological reactions
of the root. However, in the Amherst plantings where growth
conditions favored normal transpiration (high soil moisture,
low temperature and short light exposure) pithiness was
apparent at the point of top root equality and increased as
the ratio of top to root decreased. It seems doubtful, there-
fore, that transpiration plays a dominant role as a causal
factor for pithiness.

Excess carbohydrate utilization was also considered
as a possible cause for pithiness. Such a physiological
reaction may be caused by either of two growth conditions;

(1) an abnormally rapid vegetative growth, with the result
that the synthesis of carbohydrates is not sufficient to
promote such growth and, therefore, the reserve carbohydrates
of the root are utilized; (2) a slow top growth and a rapid

root development resulting in only sufficient carbohydrates

being synthesized to promote growth of the plant, leaving

no reserve supply available for storage in the proportionately
large root. In the observations made there was a definite
relation of the top and root at all times during the period

of development of the plant; as the top increased in weight
the root increased to a lesser degree or vice versa. There-
fore, if carbohydrate exhaustion of the root was in some de-
gree proportional to the increase of the top, pithiness

should conform more or less to the ratio of the top to root.
Actually pithiness increased most when the top-root ratio

was changing least.

If pithiness is caused by excess carbohydrate uti-
lization all tissue functioning in a storage capacity should
breakdown to a greater or lesser degree. This was not
true, in that the cortical region of the root never, under
any conditions, eXhibited any traces of pithiness. Also,
those varieties having comparatively small xylem parenchyma
cells and numerous vascular rays did not show extreme
pithiness, even in the maturity and seed formation stage
of development. It is doubtful if carbohydrate utilization
is primarily responsible for pithiness of the radish root.

Growth tension, by which the increase in volume

exceeds the increase in mass, thereby, causing a rupture of

the tissue in such a manner as to cause pithiness, was another
possible factor given consideration. After the initial forma-
tion of the secondary tissue there appeared to be no marked
increase in number of cells but, rather a decided increase in
the size of the existing cells, especially those of the xylem
parenchyma. Consequently if the increase in volume of cell
content is greater than the rate of increase in size of cell,
there must be a rupture of the tissue. The greater the anpunt
of supporting and conducting tissue within the xylem
parenchyma and the smaller the individual cells of this
region the more equal will be the distribution of the tension
of growth and the greater the resistance of the individual
cell. Therefore, where the cells in the xylem parenchyma

are large and have little supporting tissue, growth tension
should be greater per individual than where the cells are
small and have a large amount of supporting elements. Pdthi-
ness was always first apparent in the region between the vas-
cular rays of the xylem parenchyma. In this region are located
the largest cells. The small cells, in immediate proximity to
the supporting and conducting tissue, were not affected until
the very advanced stages of tissue breakdown had developed.

Pithiness was never apparent in the cortex where the cells were

.‘Jfl . ‘417111. .IFI.‘
.

—62

comparatively very small.

A rapid growth of the root stimulated a rapid increase
of secondary tissue in the xylem parenchyma and thereby set
‘up a radial tension outward. A slow growth of the root caused
a depletion of the primary tissue and thereby set up a radial
tension inward. Therefore, growth or increase in size, creates
a tension from within, outward or from without, inward and
that tissue offering the least resistance is ruptured and
broken.

Anatomical observations also support the tension
hypothesis in that the tissue where pithiness was apparent
had a distinct appearance of having been pulled or torn
apart.

In conclusion, growth tension appears to be the
primary factor causing tissue breakdown within the radish
root with transpiration and carbohydrate exhaustion antecedent
to it, in that, without the withdrawal of sugar there would

be less water and, therefore, less growth tension would develop:

~63

Summary

Practically all varieties of the cultivated radish,
Raphanus sativus, tend to become pithy at some time during
their period of development. The studies as reported in this
paper were undertaken in an endeavor to isolate the factor or
factors causal for this condition of tissue breakdown within
th radish root. While no definite conclusions can, as yet,
be presented, the following summary will give indications
of what the investigations have shown.

1. The quick growing varieties exhibit pithiness
much more readily and to a more pronounced
degree than do the slow growing and maturing
sorts.

2. Pithiness is associated with roots having a
narrow cortex, a cambium ring in which the
vascular bundles are comparatively far apart,
a xylem parenchyma in which the cells are
large and in which few vascular rays are
found and a stile in which the primary
xylem elements are prominent.

3. Pithiness deveIOps only in the xylem parenchyma
tissue of the storage root; and the larger the

cells accompanied by little supporting tissue

4.

-64

(vascular rays) in this region of the root
the sooner pithiness is evident and the more
rapid its deveIOpment.

Pithiness was always apparent at the approximate
time of equality of top and root weight, and
as the top-root ratio decreased the percentage
of tissue breakdown increased. This was true
regardless of environment.

High temperature, low soil moisture combined with
long light exposure tend to hasten tissue break-
down while conditions of an opposite nature
tend to retard such breakdown.

All factors of the environment influence plant
growth, however, these studies indicated that
the most important single factor governing
pithiness of the radish is air temperature.

Pithiness seems to be the effect of a physiologi-

cal variable of one or more factors causing

tension within the xylem parenchyma and, there-
fore, a rupture and breakdown of the tissue in
this region of the storage root. The investi-
gations indicate growth tension to be the primary

physiological factor causing tissue breakdown

-65

with transpiration and carbohydrate eXhaustion

antecedent to and associated with it.

Literature Cited

Bailey, L. H., Standard Cyclopedia of Horticulture,
2895-2899. 1916.

------ Vegetable Gardening. Machillan, New York
273-277. 1914

Conrad, C. M., Pectic Substances. Am. Jour. Bot. 13:531-547
1928.

Crist, J. W. and Stout, G. J., Relation Between Top and Root
Size in Herbaceous Plants. Plant Physiol. 4:
63-85, 1929.

Garner, W. W. and Allard, H A., Effect of the Relative
Length of Day and flight and Other Factors of
the Environment 0n Growth and Reproduction
in Plants. Jour. of Agr. Res. 18:11. 1920.

Gerard, R , Recherches sur la structure de l'axe au-
dessous des feuilles seminales, chez 1es
Dicotylidonees. C. r. Load. Sci. Paris 90.
1880.

Golinska, 8., Einige Beobachtungen uber die Morpholgie und
Anatomie der Radieschenknolle.
Gartenbauwissenschaft, Sonderabdruck ans 1.
Band. 5. Iieft 1929.

Haberlaudt, G. Physilogische. Pflansenanatomie
Berlin 1924.

Hegi, G., Flora der Mitteleuropea. 4

Jones, E. A., Rosa, J. J., Truck Crop Plants. McGraw-Hill,
New York. 173, 1928

11.

14.

15.

16.

_ 17.

18.

19.

20.

21.

22.

-66

Johansen, N., Einige vusuche uber die Einwirkung ver-
schiedener Belichtung auf die vegetative
Euntwicklung von Raphanus sativus. Flora
(Jena) N. r. 21. 1927.

Lloyd, Garden Farming. Lippincott, Philadelphia.
103-104. 1914.

Malinowski, E., On the Inheritance of Some Characters in
the Radishes. C. r. de la Soc. Sci. de
Varsonie 9 H. 7. 1916.

Moldenhawer, K., Uber Artkreuzungen der Raphanus und Brassica.
Ogrodnictivo Krakow Nr. 4/7. 1925.

Pearsall, W. H., Studies in Growth IV. Correlations in
Development. .Ann. Bot. 37:261—275. 1923.

............ Growth Studies 11. On the Relative Size

of Growing Plant Organs. Ann. Bot. 41:
549-556. 1927.

Riolle, Y. T., Recherches Morphologiques et Biologiques
sur les Radish Cultives. Imprimerie
Berger-Levrault. Nancy. 79-87. 1914.

Siniskaia, On the Nature and the Conditions of the
Formation of Esculent Roots. (Preliminary
Report) Bull. of Applied Bot. and Plant
Breeding. Leningrad 16, Mr. I. 1926.

Thompson, C. E., Vegetable Gardening. McGraw-Hill, New York.
249-252. 1923.

Vilenovsky, J., Vergleichende Morphologie Pflanzen 1. 1905.

Watts, R. L., Vegetable Gardening. Orange Judd, New York.
417-419. 1928.

Weaver, J. E., Root Development of Vegetable Crops.
McGraw-Hill, New York.

———————————— Kramer, J., and Read, M. Development Of

Root and Shoot of Winter Wheat under Field
Environment. Ecol. 5:26-50. 1924.

is; ._ ..-

Plate III

Sections of the storage portion of radish roots,

variety Scalet Globe of the September 9, 1929 planting, show-

ing successive stages of development. Sections are enlarged

six times.
A September

E September

A and B
C and D

E ---

F and G

In

thin cortex,

16, B September 18, C September 25, D Setpember 25

27, F September 29, G October 1

Mazatlan
--- P. C. primary cortex, C. C. central cylinder
—- Co cortical region, X. P. exylem parenchyma
Co cortex, X. P. xylem parenchym, V. R. vascular ray,
Pe Periderm, C. R. cambium ring, St. stele.
--- Co cortex, X. P. xylem parenchyma, St. stele,
Pe periderm, C. R. Cambium ring.
sections C, D, E, F and G note the thin periderm

composed of fairly large cells, the cambium ring,

the xylem parenchyma region with its few vascular rays and

supporting tissue and the prominent stele in which are located

the primary xylem elements.

PLATE III

98¢?

a

     

0

 

B

 

 

 

 

 

 

 

, ,. ,1. a If. .‘.[. 441W

Plate IV

A continuation of plate III

A October 5, October 7, C October 9, D October 9

Explanatign

Co cortex, C. R. cambium ring, X. P. xylem parenchyma,
V R. vascular ray, St. stele, Pi pithy area,
L. R. lateral root.

Eggg. The development of the pithy areas and the
comparative small amount of vascular and supporting tissue.
Section A contained more vascular elements within the xylem
parenchyma than was common for this variety and considerably

umre than was common for Frenthreakfast.

PLATE JY

cwi

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7.9..

 

 

 

 

 

Plate V

A and B are a continuation of plates III and IV for
the dates October 18 and October 26. Sections C and D represent
French Breakfast and Black Spanish respectively, planted

September 9, 1929 and sectioned October 26 (enlarged .1. times).

mm

Pe. periderm, Co cortex, C. R. cambium ring, X. P. xylem
parenchyma, V. R. vascular ray, St. stele, Pi pith.

Note the extreme tissue breakdown in sections A, B
and C and compare with the non—pithy section D; the highly
liquified vascular bundles of C; the corky periderm, thick
cortex, the comparative size of the parenchyma cells, the
distinct vascular rays and the quite inconspicuous stele of

D.

PLATE I

 

 

‘JJOD an- '- '—-* at. "-3

Plate VI

Sections of which Icicle representing A, 4 (9/9-9/13)
and B, 17 (6/80-7/17) days development of the enlarged storage

root. (enlarged 25 times)

Ep. epidermis, P. parenchyma cells, En endodermis, Pr. pericycle,

P. C. primary cortex, C. C. central cylinder, Px primary

xylem elements, P. C. procambium region, P. P. primary

phloem elements, V. R. vascular ray, X. P. xylem parenchyma,

St. stele.

Note in section B vascular element of the vascular

ray in which the tracheids are large, slightly liquified and
surrounded by small cells; the stele with its prominent
primary xylem and tracheids, and the large parenchyma cells

located between the stele and vascular rays.

 

PLATE II

 

“R

.1)?

 

Plate vii

A continuation of plate VI in which the sections
represent A, 25 (6/30-7/25) and B, 31 (6/30-7/31) days

development of the enlarged storage root (Enlarged 25 times).

Explanatig_

-*

Note the distinct enlargement of the
parenchyma cells over those shown in the sections of
plate VI. The root from Which section B was taken
exhibited 40 percent. pithiness, although no pithy areas are

shown in this section.

 

 

 

ifl- all

Plate VIII

Sections of Scarlet Globe representing A, 4(9/9-9/13)
and B, 9 (9/9—9/18) days development of the enlarged storage

root. (Enlarged 25 times).

Exglanation_

 

P. C. primary cortex, C. C. central cylinder, p, x, primary
xylem, St. stele, Pr pericycle, S. P. E. secondary cortex
and phloem elements, 0 cambium, S. X. E. secondary xylem

elements, P. X. E. primary xylem elements, T. tracheids

 

PLATE SEED

 

 

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Plate IX

Sections of Scarlet Globe representing A, 14
(9/9 - 9/23), B, 20 (9/9-9/29), c, 23 (9/9-10/2) days develop-

ment of the enlarged storage root. (enlarged 25 times)

Explanatiog

St. stele, T. tracheids, V. R. vascular ray, X. P. xylem
parenchyma, C. R. cambium ring, S. E. supporting elements.
Note in section B the mass of small, someihat
thick walled supporting tissue; the development of pithiness
in section C. in Which A shows the tissue between two cells
before breakdown, B the rupture of the tissue between two

cells and C a fair sized pithy area.

 

 

 

 

PLATE IX."

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Plate X

Sections of Giant Stuttgart representing A, 14
(9/9-9/23) B, 18 (9/9-9/27) and c, 28 (9/9-10/5) days develop-

ment of the enlarged storage root. (Enlarged 25 times).

Explanati.‘

Sc. Pe. secondary cortex and periderm, Pr. pericycle,
P. X. primary xylem, S. X. secondary xylem, C. cambium,
S. P. secondary phloem.
Note and compare the cell arrangement and the size
of the cells of these three sections with those of plates

V1, VII, VIII and IX.

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Plate XI

Sections of Black Spanish representing A, 23 (6/30-7/23
and B, 81 (6/30-7/31) days development of the enlarged storage

root. (Enlarged 25 times)

Egplapation
V. E. vascular elements, X. P. xylem parenchyma, P. X. E.
primary exylem elements.
Note and compare the cell arrangement and cell size,
the small amount of primary xylem elements in the stele and the
ratio of vascular elements to parenchyma tissue of these sections

and those of plates VI, VII, VIII, IX and I

a. - as 0-4 .

 

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