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ANATOMY OF PHASEOLUS YULGARiS
L. VAR. BLACK VALENTINE

THESIS FOR THE DEGREE 0F PH. D.

I‘flargarct T. Dcutt
1933

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A?.~LTCL.Y OF HELSECLUS "RTIBu—LRIS L. VAR. BLACK VALE L.‘ If;

 

 

Doctor of Philosoghy

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Intro~uciiox
Luterial usd hethous
Gross horpholopy
anatouy
Root-
Stem
Leaf
Stipula
Cotyledon .
Ontogeny
Root
Stem
Seccndary Roots
Adventitious Roots
Trunsit‘on He;ion
Leaf
Coursa of Vascular ;undles
Root, Transition Re;iou, First Node
Seco 1d node
Chird node
Branches
Staple Leaf

Comyound Leaf

Flowsr
311mm 1*;7

95503

Literature Cited

Explanation of Eldtes

ACI ENC ”mi 121‘} ‘1“ S

The writer is greatly indebted to Dr. E. A- Bessey

and Dr. E. F. Woodcock of hicLi an State 30113 e .or helpful
criticisrs and advice durinp this isvestigation and in the

of the manusc:ipt. The writer is also very grate-
ful to Dr. Rey Kelson for the prereratiun of the rhetouicro—

. w .-, , p,‘ ‘ .: -, a. i, , -_ . ,.
grupns aufl for Si,¢estiors 1A regsrd to the 91¢

mm Y 03‘ 313.9931“... 3.3 meals L- M- new- w 4.211.123.-

.1.n.3.r.o_d.u_c.t.i.o.n.

The first anatomical worh on the genus Phaseolus was published
by Nageli (1858). He used two species, E. vulgar_is_ and P. “ulti_1oius,
in his investigations of the course of the vascular bundles in the stem.
Van Tieghem (1871) was interested primarily in the structure of the root
and studied it during both primary and secondary growth.

It was not until 1872 that any very detailed studies were made
on the anatomy of ghaseolus_zul£aris. In that year Dodel (1872) pub—
lished an extensive paper dealinr Viith the course of the vascular bundles

as well as with the structure of the tissues; however, this was only in
the hypocotyl and root. Petit (1887) and Plitt (1886) investigated the
petiole of the bean, and de Fury (1% 4) the differentiation of tissues in
the root tip.

De Bold (1894) worked on three hundred srecies of the tribe
Ihaseolae)in an attempt to obtain anatomical criteria for the differen-
tiation of the species. In his systeiatic work on the dicotyledons,
Solereder (1908) pointed out various features of the anatomy Cf.§i§§§2l32
Eagle-

MOre recently)Comptou (1912) carried on an extensive study of
the seedling structure of the Leguminosae. Harris (1921) investigated
variations in the number of vascular bundles at different heights in seed-
lings. Within the last few years)nany studies have been nade on bean
mosaic, a virus disease of rreat economic infortance.

T} ' sudy of Phas eolus 1"““lo 1‘;as been made with t1=.e Iurpase

—.....-M--. mm‘

of tracinr the course cf the vascular tissue throurhout the plant, and of

studying the development of the various tissues. The writer has endeavore;
to make this as complete a study as possible, with the idea in view that
such an investigation of the normal structure of the plant may prove to be

of value to those'working on the mosaic an other diseases of the bean.

Katerial and Fethcds

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The material for study was obtained from plants grown in the
greenhouses at Kichigan State College and at the University of California.
The §g£g%1;@§g§gg§ge'variety was used in the investigation. The material
was fixed in chromacetic acid, and the microtone sections were stained
with Delafield's haematoxylin and safranin. PhJOTOflUCln and hydrochloric
acid were used for xylem studies in the free-hand sections. Portions of

the plant were cleared by using equal parts of turpentine and phenol.

--.—.~.v——

 

Phaseolus YB$£E£l§.L° var. Eléfigllélfifléiyén a nenber of the
Leguminosae, is a dwarf bean, twelve to fourteen inches high, and erect
(Jarvis, 1908). The root system is fibrous; the primary root persists
but is equaled by the secondary roots. Adventitious roots commonly arise
frcm the lower portion of the hypocotyl.

The stat below the cotyledons, i. e. the hypocotyl, is round in
cross-section, and especially enlarged in the lower portion. Above the
cotyledons)it is.more or less annular or ridged. The cotyledons are epi-
geal, and oppositely arranged at the first node. The first leaves to
develop appear at the second node; they are simple and also opposite. The
base of each is deeply cordate. The subsequent leaves which develop are

all compound, composed of three leaflets, are they have an alternate

arrangement on the stem.
The petioles of the leaves are enlarged for a length of two
millimeters at their base, thus formizr a definite pulvinus in this

region. Above the pulvinus the petiole in cross section is round except

)
for a groove on its ventral surface. There is present on either side of
this depression a wing or ridge)Which ends in a stipel several millimeters
from the base of the blade. The leaflets of the compo nd leaf are shortly
petiolulate. The margin of the simple leaf and of the leaflets is entire.
The venation of the leaves is of the netted type and the rain.veins are
three in numb r, branching from the same point at the base of the blade.
Lateral branches arise from these and anastonose.

Stipules regularly occur in connection with both the simple and
compound leaves. Two ovate, acute stipules originate at the base of the
petiole of the compound leaf. at the second node, where the two pposite
leaves are attached, there is one pair of stipules. It is interesting to
note that each of these is double—toothed at the aperibut united at the
base. Perhaps these represent ta) united stipules. Stipels occur at the
base of the leaflets of the compound leaf. a pair is evident at the base
of the temninal leaflet)and on the petiole where the two lateral leaflets
originate.

The flowers are born in small racenes, the peduncle arising in
the exile of the leaves. The pedicels of the flowers bear bracts at the
point on the peduncle from which they originate. a pair of bracts also
occurs just beneath the flower. The flowers are papilionaceous, consist-
ing of five united sepals, an irregular corolla of an outermost large

standard, a lateral pair of clawed wings, and the innernost pair of petals,

united and pressed together over the stamens and pistil to foam the keel.
The ten stamens are inserted at the sane height as the corolla and are
diadelphous, nine being united)with the tenth one free. The pistil cen-
sists of a single carpal; the style is rolled. In fruit, a typical

legume or pod is formed, which encloses the shiny, black seeds.

A cross section through the primary root, at a stage when
secondary Frowth is just beginning, shows a central core of vascular
tissue which is limited on the outside by the endode-mis and cortex
(Plate I, F). The vascular tissue has a tetrarch arrangement. In the
phloem, the nest evident cells are a group of thick-walled fibers, which
are 1 n5 and pointed. Just outside of these is the more or less crushed
protophloem, and inside, the remaining primary tissues of sieve tubes,
conpanion cells, and a few parenchyma cells (Ilate IV,(;)-

The protoxylem elements of the oxarch xylem are snail and
spirally thickened. The netaxylen cells are larger and pitted. n cam-
bium layer lies between the Xylem and the phloen.

The pericycle consists of one layer of cells Opposite the
phloem, but several rows opposite the xylen. a sinile row of endodernal
cells separates the vascular cylinder from the cortex. The cortex con-
sists of fifteen or sixteen rows of parenchyna cells, among which are
intercellular spaces. This is bounded on the outside by the root epi-

dermis, which sloughs off early.

Since the transition region at the base of the hypocotyl lel
be taken up in detail later, only tte portion of the hypocotyl which
shows a typical stexzstructure will be described here. In this rerion,
below the cotyledons, a rinr of collateral bundles surrounds a large cen-
tral pith (Plate I, Gd. The xylem of these bundles has a tangential
arranfenent rather than a radial such as occurs in the stem above the

F7

cotyledons (Plate VII, a,- ihe xylem is endarch. a f scicular canbium

:11

o
f.)

separates it from the phloem, which is marked by large, darkly staining
tannin sacs, which are not found in the loot. These sacs are elongated
cells with transverse cross walls. Surrounding each is a ring of paren-
chvna cells. Sieve tubes and conpanion cells make up the renaining tissue
of the phloem. The sieve tubes are cylindrical cells with transverse end
walls. The entire transverse wall consists of a sieve plate (Plate III,D)-
They are found also in the longitudinal walls (llate III, F). Although
sieve plates occur in the primary sieve tubes, they are nuch nore notice-
able in secondary tissue. This is probably due to the {raster number of
secondary sieve tubes in relation to other phloem cells.

In addition to the bundles composed of primary rylem.and primary
phloem, there occur between the larrer ones, small bundles which consist
of prinary phloem only (Plate V, G).

The pericycle, in the fern of a cap over the phloem of such
bundle, consists of several rows of fibers)whose walls are not lignified
until secondary thickening occurs. Ectween the bundles the pericycle
consists of parenchyma cells which are continuous with those of the rays

and the pith.

The cortex, as in the root, consists of several rows of larpe
parenchyma cells, and from the epidermis arise hairs. The cells of the
epidermis of the stat are elongated in the direction of the long axis of
the stem, and their walls in surface view are not undulete. Stomata occur
in the epidermis of the stem.

above the cotyledons tie vascular bundles are collateral, and the
xylem extends toward the center of the stem parallel to the radius instead
of tangential to the radius as 'n the rerion below the cotyledons (Plate I,
H). In the 'nternode between the cotyledons and the prinary leaves, there
are always twelve bundles. The six larger bundles occupy the six ridges
or angles of die stem)and alternate with six snall bundles. The tissues
are similar to tlose in the hypocotyl, but the pith is considerably
meller. The six large bundles form the leaf traces to the primary leaves
(Plate V, U). Above the prinnry leaves,the stem is marked by five more or
less distinct ridges)which mark the position f the five large bundles
that form the leaf traces to the compound leaVes (Plate I, C). The number
of bundles is somewhat variable at this point.

The branch traces oriyinate in the exile of the leaves as branches
of the individual bundles on either side of the gap left by the median
leaf trace (Plate I, D). The vascular system of the branch is, then, con-

nected to trst of the main stem by these two bundles.

lea:
In a cross section of the pulvinus (Plate II, D), it is evident
that the vascular cylinder consists of a united ring of tissues compressed
into a Snell space in the center)with only a very srnll pith. The cortex

is very thick,and consists of ei;ht or more rows of parench*na cells. bhen

the leaf traces first enter the pulvinus, the vascular elements have an
amphicribral arrangement (Plate II, R, C), but shortly, after some
anastomosing, they assume a collateral position witi the phloem toward
the outside. The endodermis surrounds the united circle of conducting
tissue)and delimits it fr m the cortex.

As the top of the pulvinus is reached, toward the narrowing of
the petiole, the circle of vascular tissue breaks up into definite,
separate, vascular bundles. A furrow gradually develops on the ventral
surface of the petiole, and a narrow wing develOps on either side. Thus
sections from the middle of the petiole show a ring of separate vascular
bundles, eleven in number in the compound leaf. The circle is not con—
plete on the ventral side, opposite the furrow, but is separated by a gap.
Two of the eleven bundles lie in the wings, each forminr a trace to one
of the stipels; these traces are amphicribral. The other bundles of the
petiole are similar in structure to those of the stem. Their xylem con-
sists of small protoxylem elements, metarylem, and a few secondar' vessels
and tracheids. In the phloem are sieve tubes, conpanion cells, and large
tannin sacs. Each bundle is capped by a Croup of pericycle fibers. Only
a narrow cortex of one or two rows of cells surrou;ds the stale, except
on the wings and to the outside of the five larfe bundles. The collen-
chyma tissue opposite the bundles consists of several rows of cells; in
other parts it consists of but one layer. An epidermis with stomata sur-
rounds the petiole.

The structure of the petiole of the sinple leaf is similar to
that of the compound leaf, except that there are but nine bundles instead

of eleven.

The mesophyll of the blade of the leaf consists of a palisade
layer and a spongy layer (Plate VI, C). The palisade tissue is in the
form of a single layer of elongated cells arranged perpendicular to the

epider.is and separated by only a few intercellular spaces. These cells

)
are in contact with the spongy parenchyma tissue, whose cells are irre—
gular in Shape and arrangenent, and which has large intercellular spaces
and chambers. There are usually not more than four layers of cells in

this spongy tissue, and the chloroplasts are not as numerous as in the
palisade tissue.

The cells of both upper and lower epidermis appear deeply undu—
late in shape in surface view (Plate VI, J). The thickness of the upper
epiderniS is about one and one-half times greater than that of the lower
epidermis. Some of the epidermal cells are modified in several ways, and
so show variation from.the typical shape and arrangement.

A pair of guard cells containing hlorophyll surrounds each
stoma, but no accessory cells are present. Over the veins the epidermal
cells are much elongated parallel to the longitudinal axis of the veins,
and their radial walls are mostly straight. The cells in contact with an
epidermal cell which has given rise to a hair differ from adjacent ones.
These surrounding cells are elongated, have straight valls, and radiate
from the hair cell (Plate VI, I). No chloroplasts are found in the epi-
dermal cells, aside from the guard cells of the stomata.

There is considerable Variation in the number of stomata occurring
in the leaf epidermis. They are nore numerous on the lower surface, ave-
raging there, in nature leaves, about eighty—five stomata per Square milli-

meter. Cn very young leaves, two hundred and fifty stonata may occur per

square millimeter, but as the epidermal tissue increases in size, the
stomata are pushed farther apart. Thus in still young leaves, but older
than the former, there will be but one hundred stomata per square milli-
meter.

Hairs of several kinds are common, especially on the younger
plants. Aside from the root hairs, three main types may be distinguished,
occurring on the stems, leaves, stipules, and other parts (Plate VI, R).
The longest hairs which are found are strai3h , taper to a point, and
sometimes are 400 microns in length. They consist of three cells, two of
which are basal and short, the third being long and terminal. Then there
are the hooked hairs, similar to the first)but whose end curves; these are
the "Klimmer" hairs of de Bold. The glandular hairs are short and club-
shaped,.consisting of a number of cells, and usually are about 60 microns
long. No hairs are found on the cotyledons or corolla, but they are connon
on all other parts of die plant, especia ly along the veins of the leaves.

The vascular tissue of the blade is a continuation of that of the
petiole into the midrib. The midrib projects promineLtly on the lower
suriace of the blade,but less so on the upper surface. The vascular tissue
has the same general arrangement as in a bundle in the petiole. In cross
section it has a semicircular form with the Open part toward the upper sur~
face. The vascular elements consist of xylem and phloem with a cap of
fibers over the latter. The structure of the branch veins is essentially
like that of the midrib, from which they have arisen. As the veins get
smaller, the amount of xylem and phloem decreases accordingly until
finally all the phloen.disappears, and only one or two spiral elements of

the xylem regain surrounded by conducting :arenchyna.

5

aiirales.

Since the stipules may be considered as a part of the leaf, their
structure should be treated here. As has been stated previously, the sti—
pules at the base of the petiole of the simple leaf are two-toothed at the
apex and united at the base. The vascular supply consists of two traces
which originate as branches of he two lateral leaf traces as they pass

into the petiole of the leaf. Since in the compound leaves there is a

pair of stipules for each leaf, it is probable that those at the base of
the sinple leaves represent two which have become united.

The stipules of the simple leaf have a mesophyll tissue which

‘7‘

consists of spongy parenchyma, with -o palisade cells (Plate VI, i).

U

Usually it is under the stomata that nest of the air spaces occur. The
veins are similar to those of the leaf, but the amount of each tissue is
reduced. There are two main veins, each runninr out to the apex, and a
smaller vein along each margin. The stipules of the ccmpOind leaf also
consist of sponry parenchyma, but it is hora loosely arranped than in the
stipules of the simple leaf. hour Kain veins furnish the vascular supp y,
with a smaller vein on each nursin.

The stipules are cOVered with an epidermis, the cells of which
differ from those of the leaf blade. They are slightly eloniated parallel
to the long axis of the stipule, and their radial walls are not undulate.

Stomata are bore abundant in the lower epidenmis than in the upper.

Cotyledons
a cross section of a cotyledon.shows that it consists of large
parenchyma cells with thickened walls and numerous pits. (Plate VI, D, E).

The intercellular spaces are small in ccmparison with those present in the

-11-

leaves. The cells of the epidennis have strai.ht radial we lls (Plate VI,
h). The cells of tie upper epidermis are much flattened, while those of
the lower epidennis are almost isodianetric. Stomata occur only on the
lower epidermis. The vascular tissue is sinilar to that of the leaves,
and is derived from two traces from the hypocotyl. It is interesting to
note the larger number of starch grains and of aleurone grains in the
hmaediate vicinity of the veins in the storage parenchyma cells. K0 heirs

of any kind project from the cotyledons.

CntoreIIy

has

A longitudinal sect ion throurh a woulg root shows that it is com-
posed of very definite parts. at its tip is the root cap, of acre or less
loosely arra aged cells, and directly behind this lies the region of rapid-
ly dividing promeristem. From this region the cells show a gradual elon-
gation and enlar5emcnt until finally the raature condit in n is evident at the
base of the root.

Behind the root cap, three regions are distinct (Ilate IV, B),
the dermatogen, a single layer of cells at the outside; the periblem within,
which later forms the cortex; and finally the central resion of slightly
elongated cells, the plerome. About one and a half millimeters behind the
root tip in the plerome, the central cells have increased in disr‘ieter and
have elom sated to five times their diameter. Outside of these pith initials,
lie four strands of long’narrow,densely protoplasmic cells. These are the
cells of t1:e procanzbium llCh give rise to the phloem. They are seven to
ten times as lone as wide. In cross section these strands appear as groups

in the four corners of a square (Pl its 17,4). Between these groups or

this stare, the endodernis and pericycle cu“: ot 1e ver' readily distin-
guished from the surroundinr cells of the periblen. The dernato
fairly well marked off from tte other layers, its cells having divided by
enticlinul Wells only.

Although tke phloem is the first of the vascular tissues to
differentiate, it is extremely difficult to follow the steps, due to the
1nconsgicuous differences betwec n the protophloem and the procemtium.
Ho.vever in sections where it is evident, one or two cells ne1:t to the
pericycle in each of tee four procsnhium strdnds show slightly thicker
walls.

Simultaneous with he formation of tne first proto; hloem eleme 11ts,
tl1e first xylem cells di1 ferentiate (Plate IV, C). lhe trotoxyle1 can he
reCOgnized by the notices ble thickening of the cell walls>and by their
spiral thickenings (Plate III, 3). By the time the protoxylem forms, the
pericycle and the endodermis are more definite. In the region of the
phloem, the pericycle co :1sists of but one layer of cells, one and a half
to two times as long as wide. The cells of the endodermis in longitudinal

sections appear sli(htly longer tren.ttose of the pericycle.

The rerzeining protoxylem cells raridly differentiate centri-
petelly, thus naking the xyla. e:arc h. These late r fo fined cells are
larger in diameter than the first to differentiate, with spiral thickenings
more closely arranged, and pass over into the reticulute types. Leanwhile,
Lore sieve tubes and companion cells of the protophloen form (Plate IV, D).

Then some of the proceimliuv cells of the

"1

hloem re ion elonrate, their end

1

wells become oblique, and their walls thicken to form the first metephloem

fibers, which lie adjacent to the protophloen (Plate IV, E). Ketaphloem,
consisting of sieve tubes, companion cells, and parenchyma cells differ-
entiates to the inside of the fibers. The parenchyma cells between the
Kyle; and the phloem strands increase in number.

Along with the development of metaphloem occurs the differentia-
tion of the metarylem)whose cells have a much arger diameter than those
of the protoxylem and have numerous simple pits (Plate IV, F). At this
time’s cross section of a root shows four well developed arms of xylen,
with four alternating groups of phloem, the latter well marked by the thick
walled fibers. lhen the walls of the cells occupying the central portion
of the root thicken, lignify, and becons pitted, thus ferding a solid center
of conducting tissue (Plate IV, G). as a result of the increase in size of
the cells of the vascular cylinder, the few we of protophloen cells lying
between the pericycle and the fibers become crushed and the cells in some
cases are entirely obliterated, even before secondary growth has taken
place.

The cells in other portions of the root have undergone little
change except in size. Intercellular spaces have appeared in the cortex.

At this stage of development some of the parenchvna cells between
the phloem and metaxylem divide longitudinally by tangential walls. A row
of the cells of the pericycle just outside of the protoxylen likewise divides,
and thus the cambiun.layer develOps by the reversion to meristem of these

parenchyma cells.

Secondary Growth in the Root

--—--. u..- c... ----—. - - m

 

 

host of the tissue of the nature root is secondary. In contrast

to the snell vascular cylinder of the prinary root surrounded by the thick

-14-

cortex, the nature root consists of a very narrow cortex surrounding a great
amount of vascular tissue.

"he secondary xylem of the root consists mainly of tracheids and
fibers arrang d in radial rows. as in the stem, several tangential rows
of these have thicker walls,and give an appearance of annular rings.
Besides this tissue, large vessels differentiate from the caabium. These
are well provided with simple pits. Parenchyma is forned especially in
the vicinity of the vessels, but also to some extent among the tracheids.
Four broad rays of parenchyma cells are cut off by the cambium opposite
the four groups of protoxylem)and extend out through he phloem. as a
result,the conducting tissues are not continuous around the root. The

walls of the warenchyma cells eventually thicken and became lignified.

A

Most of the phloem is secondary, and much less is forked than
xylem. The protophloem is so crushed that it is no longer recepnizable.
The characteristic group of primary fibers 15' unchanged. The secondary
phloem consists mainly of sieve tubes, companion cells, and only a few
parencbyma cells. Sieve plates are common.

The cells 0 the cortex, as well as those of the pericycle and
endodermis, are crushed and flattened due to the enormous increase in
size of the vaSCLdar cylinder. The outermost die and are sloughed off.
The epidenris sloughs off soon a'ter secondary growth begins and nothing

remains of the cortex except three or four rows of cells.

Stet;
The tip of the stem is comparable to the root tip only in the
fact that it consists of meristem which differentiates into the prinary

tissues; their arrangerent differs from that in the root. A root cap is

entirely lacking at the stan tip. is in the root, the apex consists of
thin-walled, dersely protoplasmic cells, 'hich, directly behind the tip,
begin to differentiate into more or less definite regions. These regions
consist of the dermatogen, the ;r round n.0ristem, and the isolated strands
of procambium. The cells of the procanbium differ greatly from all others
in being elongated longitudinally)and in having a sraller diazn ter than
the surrounding tissue. They also have denser protoplasm than the sur-
rounding gro ound meristem.

Almost simultaneously with the settilg off of'these regions, the
first conducting tissue differentiates from that part of the procaxbium
strand toward the center of the star (Plate V, a). This is the proto-
xylem. These elements are lonrer than the surrounding procahbium cellsz
and are characterized by seco11dary W ll thi ckenin4 in the form of loose
rings. The walls are not yet lignified. Additional protoxylem cells
differentiate centrifuge ly, and thus the xy an of the sta: is endarch
in contrast to the e: {arch xylem of the root. ine s1ccessive protoxylem
cells th at form are larger than the first, and their wall thicken nfs
are in the form of closer spirals, spiral-nets, and nets (Plate III, B).

At the same time, or probably a little before the appearance
of the protoxylem, the protophloem differentiates from the procanbium.
ihe protophloem cells are so like the procanmiunzthut it is alnost impos-
sible to recoanize them1and they soon disappear. The metaphloem is the
fi st to be differentiated clearly. In the formation of a sieve tube, a
procambium cell enlarges, elongates, and either directly forms a sieve
tube or it may divide to form a sieve tube and adjacent companion cell-

The first sieve tubes are differentiated from the procambium cells toward

the on side of tie stem and so farther development is centripetal. The
most noticeable cells to develop in the rrirmr piwloe; are the tannin
sacs (Plate V, B). Tleir fern ation is initiated :y the enor1ous enlarge-
ment of certain procanbium cells, both in len;th and in dianeter. Such
cells *ery soon become filled with material whicn stains deeply with
Delafield's haematoxylin. These tainin sacs appear very early in the
development of the phloem. A sirgle row of procanbiun.cells surrounding
a tannin sac usually enla rges, and 1: ay divide lozigitudinally parallel to
the walls of tiie sac. The inner row fonns a ring of parenchyna cells
around the sac. Isolated :arenchyma cells nay differentiate from.the pro-
cambium, and thus lie scattered throurh the phloem. By the time the
phloem has developed to this stage, the walls of the protoxylem have
becowe slightly lignified.

Tie g-rour -d meristem has alaos+ ceased to divide and has as umed
the appearance of parenchyma cells. A few intercellular spaces have
developed. The dermatogen divides only by anticlinal walls to fonn the
epidermis. The hairs appear from the epidermal cells very early. The
sinrle row of endodermal cells is evident at this time, and they are
recognized by their greater dianeter, especially in a radial direction
and by a Lrenter lenpflti than the adjacent cortical cells. The pericycle
cells of several rows are clearly marked off where they form a cap over
the phloem just under the endcdern is. In comparison with the cortical
cells, these cells have thicker walls and less dense protoplasn. In
addition they are longer and narrower.

)

This period of differentiation is followed tv one of great cell

enlargement in all tissues. The appearance ofa fascicular carbium

characterizes the next step in develo Mp ent (Plate V, C). It is forged

L

-17-

by the tan ential division of a row of undifferentiated procanbium cells
between the xy em and the phloem. Longitudinally the canbium cells are
long and narrow with sli htly pointed ends. Soon after the differentia-
tion of this fascicular canbium, an interfascicular canhium arises. It
originates by the reversion to merister of a row of parenchyma cells
between the bundles.

In the xylem region at this stage,the metaxylen.ccmpletes its
differentiation as larger cells which are characterized by their pitted
and reticulate we lls. although rest of the cells of the metaxylem con-
sist of large pitted vessels, som parenchyma differentiates, especially
around the vessels. Li n1 ification of the walls of the vessels soon
follows their differentiation. The protoxylem elements, now lifnified
also, are becomins stretched, and the annular thickenings are farther
apart.

In th e phloen all the cells have now diff «erentia ted fror the
procanhium (Plate V, C). These gPOJES are the ”soft hast" of Dodel.
Groups of sieve tubes and campanion cells occur, anon; a few pa renchyiw
cells.L'Tiie large tannin sacs, surrouided by the layer of paronchyma, are
conspicuous. Tie end walls of the sieve tubes have developed into sieve
plates.

Tie cells of the peri w3 cle have enlargje-d considerably, but the
walls of those w} cap the phloem.are 8 ill cnly Sllg ‘tly thic}:ened.
They are packed close toge+her and are angular. No intercollular Spaces
are evident. In longitudinal sections)these cells have increased in
length, and the ends of adjacent cells have shoved past each other. The

cells of the endodermal layer have increased in size, but no other hangs

is evident. The cortical cells are nuch larger than in the previous

-13-

stage, and many intercellular spaces have developed.

("

Tne last stages of primary growth are comlletod at the samJ tire
that secondary growth is initiated, and so to a certain extent the two
stages overlap. Primary differentiation ends with the complete differ-
entiation, enlargement, and maturaoion of the proto— and meta- xylem and
phloem elements. The walls of the pericycle fibers which cap the phloem
are not yet lignified. That portion of thejpericycle opposite the rays
consists of parenchyna cells which are continuous with the rays between
the bundles. The epideiiis is a single layer of cells)with fully develored
stomata. It bears numerous hairs. The endodermal cells in cross section
are elongated in a tangential direction rather than in a radial direction
as in younger stages. In longitudinal section, they are slightly longer

than the parenchyma cells of the cortex.

" __ ‘ ‘ . .1, ‘. ... ‘9-
oecondarv Lrowth 1n the ate;

‘
1 .--o

With tLe differentiation of the fascicular and the interfascicular

U)

cambium, further increase in ize of the stag ‘8 brought about by the
formation of secondary tissues by these cambiuas.

The first xylat cells forned by the canbiun ring are two or three
rows of thick-walled fibers which form a auntinucus ring around the stem
(Plate V, E). host of the cells outside nese fibers consist of radially
arranged rows of trecheids. Only a few pitted vessels are forked. Fibers
may occur among the tracheids. Often a second layer of fibers is formed
as the last layer of seccndary xylen. Tris results in giving the appear-

ance of an annual ring. The secondary parenchyma cells have a diffuse

arrangement.

-19-

Besides the longitudinal conducting system of seccndary xylem and
phloen, the fascicular and interfascicular canbiuns form a transverse
systen1consisting of vascular rays. In the xylenithe parenchyma cells of
these rays are radially elongated. Both uniseriate and multiseriate rays
are formed. In height or vertical extent, the; are six orznore cells, and

heir radial extent varies. Some of the rays are continuous through the
xylem and phloem. The multiseriate rays formed by the interfascicular
cambiun are continuous with the cortex.

Tne cambium associated with the grfiups of primary phloem which
have no accompanying Irlem, first fonts the three layered ring of thick
walled fibers toward the inside of the stem. The secondary xylem, later
fo med, like that of the primary bundles having bot. xylem and phloem,
consists of large pitted vessels and tracheids. Thus these bundles have
no primary Kyla; elements projectin: into the pith (Plate V, F).

he the secondary xylem forms, great stress and pressure are
exerted on the first foried xylem lying adjacent to the pith, finally
causing the protoxylem to entirely disappear. Remnants of the cells may
be seen, especially in longitudinal sections, where they are crushed and
distorted, and the ring and spiral thickenings are scattered. The paren—
chyma in this region of the vascular bundle is liiewiso crushed and the
walls crumpled. The parenchyma cells of the pith are especially affected,
finally resulting in the disappearance of host of the pith and thus
causing the nature stem to be hollow. Usually one or t1: rows of paren-
chyma cells of the pith which lie adjacent to the innermost xylen remain
intact.

The secondary phloem consists of [rcups of ieve tubes and com-

(I)

-20-

'1

panion cells’and a few parenchyna cells (Plate V, a). In the fornation
of sieve tubes and companion cells a canbium cell enlar;es slightly and
then undergoes several lonritudinal divisions. The first divisimi is
usually in a radial direction, forndng two sieve tube mother cells. Of
these, each may then cut off a small companion cell by another longi—
tudinal division. Sieve plates in the transvers walls of the sieve tubes
are conspicuous and numerous, and they occur also in the longitudinal
walls. No secondary tannin sacs are formed. Like the protoxylan the
protophloem becomes crushed an absorbed, and as the secondary tissues

increase in amount, much of the yrimar; be macs an unrecocnizuble mass,

(3

pressed against the cap of tericycle fibers.

Th fibrous tissue of the pericycle,wiose cells were only
slightly thickened at the end of prinary growth, bear thick litnified
walls with minute lumens at he end of secondary thickening. they never
form a continuous ring of tissue around the sten, being interrupted by
the parenchyma tissue opposite the rays.

The endodermal cells during secondary growth flatten out and

p.
'"3
O

crushed, due to the increase in thickness of the stem, and at other tines
'uishaule from the cells of the cortex. These cortical
cells, as a result of the stress of the enlarging tissues, lose their

shape,and are much flattened in a radial direction.

Secondary Roots
Secondary roots arise very early in the differentiat CL of the

primary root. In some cases these roots become much more ccnspicuous

)
than the primary root. They arise in the usual manner, endogenously, by

t.e reversion to neristen.of the pericycle cells Opposite the protoxylem.

Thus the organization of the primary structure of the main root predeter—

mines tfe errangement of the secondary roots into four longitudinal rows.

Their structure is similar to that of the rain root, althourh the amount
of

of each tissue is less, as for instance, the number rows of parenchyna

cells of the cortex is such reduced, often to two or three rows.

Since the various tissues in the Kain root first develop behind
the root tip, the differentiating vascular elements of tfe young econdert
root are continuous soon with those of the nsin root. the four phloem
strands of the secondary root join at different levels with adjacent
parts of two strands of the main root. The Eylem is continuous with but

H

the one group of the primary root (Plate I, F).

Adventitious Roots

—.—-— .-

 

Adventitious roots are commonly found on the lower part of the

hypocotyl. The; are similar in structure to the true secondary roots

.1

(those origi-eting from the root and arise endogenously from the peri-

O

b
cycle. Likewise)the region from.which each ccmes is always Opposite one

of the four grou,s of nrotoxylan cells which in the hyuocotVl are cndarch.
.0. ’ c d

Transition_Re§ion
The chance in the arrangement of the vascular tissues from that
which occurs in the root to that in the stem takes place in the lower part

of the hypocotyl. The typical sten arrange ent of collateral vascular

The four protoxyle; Lroups in the root fork gradually, due to the

.lateral differentiation of procanbiun cells into xylem, and the tan forks

-22-

swing laterally, finally separati n; entirely. Thus are formed eight groups
of xylem in cross section views, he elorsn.s not arranged parallel to the
radius as in the typical stenist ucture, but tangentially (Plate I, G).

The phloenu during these xylem changes, at first broadens nit
tangentially frcm.the four groups alternating with the xyleHLin the root,
to four bands of tissue to the outside of the xylem in the lower portion of
the hypocotyl. Finally, at the time the eight *roups of xylem form, each
of the phloem bands becomes divided, thus forming eight groups which lie
over the eight xylem groups, with the collateral arrangement of tissues.

Although the tissues in the hypocotyl actually have a collateral
arrangement, it is not similar to that of the stem because the xylem has

a tangential arrangement, not radial.

Leaf

 

In a young primary leaf, still fol de 1 between tie cotyledons,
diff erentiaticn in tlze meristem tissue has already begun (Plate VI, A).
In a cross section, the upper and lower epidermis are distinct, and the
cells beneath the upper epiden.nis are slightly elongated perpendicular
to the surface. The cells of the future spongy nesophyll are still

figiltly packed to etiwer) ith no intercellular spaces. The procambium

strarfls are evident and teginning to differentiate in t the initials of
the vaSCnlar tissue. Only very few hairs h ave developed.

At a later stage,then the leaves are uegiz ining to unfold above
ground, the palisade layer has elongated to three ti es its length in the

previous stage (Plate VI, E). Stomat have develo

rd
:2 .1
(2’
£4
d

the spom y
mesophyll, although its cells have assuned various shapes, have as yet no
intercellular spaces. Hairs of the tires types prevLously mentioned are

well deVeloped.

The development of the stomata from neristem is evident. Surface
views of the epidermal tissue from.the Plumule while it is yet enclosed

g" ht

within the seedlshows it to be ccnposed of small isodiametric cells, ei
to twelve_microns square with no indication of even the initia stages in
the fornation of stomata (Plate VI, G). However, as soon as germination
takes place and the primary leaves emerge from‘between die cotyledons,
early stares in the development of the stomata occur (Plate VI, E). A
.1»

meristem cell enlarges to about twenty nicrons4tangential extent, (nd it
is cut by an antielinal wall (1), curved toward the center of the cell. In
this cut-off cell)another curved anticlinal wall (2) appears. ”hen a cell
arises within the last formed cell by the formation of still another anti-
clinal Wall (5), which curves out noticeably from the previous wall. This
last cell is the mother cell proper of the guard cell, and it is elliptical
in shape. The mother cell divides by a longitudinal radial wall (a) into
the two guard cells, between which the stonatal slit later appears. fhe
guard cells and surrounding epidermal cells increase in size. (Plate VI, I
and J).

The structure of tte me are leaf has been described already in the

discussion of the anatcny.

Coursemgf_§he Vascular Zundlg§_

W.-

 

+3

his description of the course of the vascular bundles will be
taken up under several headings)and will be followed by a sunmary to
emphasize certain features. Since the root and transition region are the
organs where the tissues are first differentiated, they will be taken up

first.

()1

Root, Transition Refiiijfinfilg FHIEEEEEE

 

The course of the bundles in the root is sixilur throughout its
length, four strands of xylem alternating with four of phloem (Plate VII; n).
The first evidence of a clan:e occurs in the lower part 0 the hypocotyl,
when each Of these strands divides, tliu forming eight strands of xy
and eight, eventually, of phloem. Only the ei ht xylem groups, which will
be rePerred to as prinary bundles, l, 2, 3, 4, 5, 6, 7, and 8, are shctn
in the figure. At the pe int where this division t1kes 1lace, there appear
the “Zwischensstranne”, or intercelary bundles of Dodel and other investi—
gators (Plate VIII, 1, 9 and 10). ese b1n1-c es, ccnsistin 3 of several
metaxyla: cells, but no protoxylen, and a few phloem cells, seen to have a
"blind" origin, there being no connection between then and the primnry
bundles. Their nurber varies; sometimes there are as rm °ny as three,
usually, however, only one or two, anl in rnny cases, none. These inter-
calary bundles uni+ e with the primary bundles which pass out into the
cotyledon8)and never continue abo ove the first node.

Just below the first node, the greater part of two primary
bundles, lb and 2b, and 5b and 6b, passes out into each of the ne -1rly
Opposite cotyledons. These, just before they turn into the cotyledons,
each form branch bundles, 13, 2a, 5a, and Ca, winch unite with adjacent
bundles and continue into the internode abOVe. The cotyledonary traces,
after traversing the cortex, unite e,and t1en at tie base of tile coVyledons
divide to fo I'm thr e bundles, w‘d d1 continue into the co file-dons.

The four remaining prinary bundles, 3, 4, 7, and 8 continue their
passage throu h the hypocotyl unchanged until several millimeters below

the cotyledons: y node. There each splits into two farts, for exazrle, 7

into 7a and 7b and 3 into Ba and 3b, and the halves 7a and 3a nearest the

J
cotyledonary -r1ce8237ing over until they are adnate with the cotyledonary

M

races lb and 2b. After the passinn 011 of the traces into the cotyledons,
hese bundles turn back into position and continue into the next internode,

united with 11 and 2 ranches of the cotyledonary traces, and are now

{9
¢
(D
(1‘

designated as 17a, 23a. 86a, and 451. These four bundles fonn the ls teril
traces to the simple leaf at the second no e. Ihe retaining halves of
the prinnry'bundles 7b, 8b. 3b, and 4b, units at the node to form the
la rue humidl 75b and 34b. These two large bundles form the median trace
of the three which pass out into the OgrOSlte single leaves of the second
node. At the node and innediutely above it’six snell bundles alternating
with the six large ones)arise as branches from the large ones. The nest
frequent manner of this b3nnclin' consists of the following: 23b and 45b
brench frcm.bundles 25a and 45a; 170 and 83c frcr buxzdles 17a and 80a; and
17b and 86b from 171 and 861. There is same variation in t1 is, due to the
fact that 17b and 86b seem to have the ability to appear as branches froa
either 23a or 17a, and 863 or 45s. These twelve bundles, tren, are those
found in the internode above the cotyledons.
The hypocotyls of r ny p111 s that were exs1ined sh r a vascular
syotn; slightly different fro: tint described above. The bundle course
of su h hypocotyls is ot identical on the tea s'des of the stem below
the cotyledons. Ehe prinary bundles 7 and 8 Franco to form 7a 7b. 83,
end 3b sooner sud consequertly further below the cot; edons than do he

prinary bundles a and 4 on the opposite side of the h my cot

point of difference lies in th fact that the shell bundles 17c and 86c, on

this snie side of the hygocotyl, arise as branches of 73b 1*d not £10m 17a

Dodel, workinr with1h_1eolus vul _aris considered t3.e cotyledon-

ary trace to consist of two e1 tire bypocotyl Eundles, and in addition one

brz1ne: fromreach of two other bundles. In the present study)suen a con-

dition never use found; in eveIr case the cotyleionery truce ccnsisted only

I."

of the greater

Pf ’

ortion of two Lypocotyl bundles)in addition to the inter-
calary bundles.

harris (leal) described the cotyledona‘y trace as nede uy of but
two bundles of the hvpocotyl, the whole of unic: oundles fo:us the trace.
This investigation shows that e snull branch from e; h of these two bundles

unites with tie two adjacent hurdles.

Secord ode

T} twelve bundles pass unchanged from the first node to tte

second M‘CQ wlere the ozpo site snL.-° ls 1ves er: found (flat ’JIII, x).

‘

~ *: M 1:1 nan
1ea111 candles Von 11d eve

5

rs belOJ the latter node the

C1
(3
4
(D
.1
{D
H
t. .
L:
H
1 .J
ti.
CD
C?
(D

beiin to swin out thr011: h t e certs")and 1 tLe node pass into the basal

part of the petiole. The lateral tra es :Je, 45a, l7e, and 251 each

branch,and form a complete sirdle Ground the node. For instance, 453

divides into din and 43 x; diu asse under the bundle Sex and forms one-
J

n1lf of the latei'al leaf trace, 80x forming the other half. The bundle

45x passes to the oruosite leaf and ferns half of the lateral leaf trace

there. he othe tiree lateral traces lr1113h in a similar gunner. Thus

H:

vi-

the vascu 1r supgly to euoi1simyle lea ac 1ullg consists of a median
bundle and two lateral bundles, each formed in the manner just described-
On eit her side of the sten at the second node’s stipule occurs.

two bundles wLich

\l‘
(E
y.._a
C.
(D
H
C I
O
H
P
f.)
{:5
L.

Ile vascular suprzlv of ea ch of the

(I)

brunch frcm tke lateral leaf traces us they a: 1i retin; thron;h the

Th six smaller bundles which have not entered into the fcrtntion
of the vascular surply of the leaves at the seCond node,end wlicn alternate
witn the six lnrée leaf trace bundles, each fore, thus naming twelve bun-
dles above the second node. However, this Lumber cran;ss very soon, for
four of the bundles divide once morezinto 173, 17h. 170, 17d, and 36f,
86g, 831‘1, end 83!, forming a total of si: tee: bundles in the stem between

the seccn' and third nodes. ”he sixteen bundles often do not erpeer until

,4.

(1

directly below the hird non de, sine frequently ;3e four bundles branch at

various Mei hts in different plunts—.
"‘1:

1n- writer's studies on the derive t:icn of the vascular traces to

the prinsry leaves do not agree witl those of Keyeli.

third Node

 

Of the sixteen bundles usuilly found below the third node, five
are lerger and act as tra es to the compound leaf (Pl ute VIII, E . Bundle
45c is thetmedidn bundle vfliic: pusses into the petiole, a:fi 86f, Edi, 17h,
and 25b are the four lateral traces. ls thee five inn dles pass into the
-e, an incowplete girdle is foraed ar0U1d half the sten.
11c stipules on either side of the stcn;obtain their vascular sup-
ply from the lateral bundles of fl1eleef traces in the fo: m of branches from

t}; en. a 5 they

(I)

.as into the petiole.

Pri

Directly above the third lode, elev1n bundles e1 9 found. Very
soon, however, bundles 45b and 23c divide to foni 43d axd 43e,end 23d and
23s. l‘hen 4Je and 23s again divide. Thus esove the third node)there are

15 bundles in a cross section of the stem.

The nodes above he third, at w} icL conp011nd le ve s originate,
have the sane g3 en2ral structure, and into each leaf pass fi 1ve bundles,
just as into the lea at the third node. I? ere is co1sideraL1e Variation
in the number of bundles in the internodes at different heights.

Several cases have been found in material investigatedjwhere,
instead of the normal five bundles passing into the petiole of a compound
leaf, there are six. In such cas es, the presence of the extra bundle
seems to be correlated with a variati n in the external no orpholOLy of tie
leaf. n these cases it consists of the appearance of an extra leaflet,
reduced in size, just at the base of the petiolules of one of the lateral
ls ea lets.

ilthough the compound leaves are ntrmally alter mtely arranged
on the st 1, two plant have been found)which at the fifth node bore a
pair of Opposite compound leaves. Sections of the node showed that
seven bundles in the stem formed the traces to thesw leaves, three and a
half bundles passing into each petiole.

Lageli reported that either four or five bundles formed tn
traces to the conpound leaf. The fou; tundle condition he not bee;

found in this investigation.

Brews
Ike vascular sup;ly of file branches niich aris; in the exile of
the leaves)is derived from branches of tie two bundles of the stem which
border the rap made by the Izedian trace of the leaf (Plate VIII, B).
These two bundles’ulich always originate at or immediately below the

node that bears the shoot divide to form a rin.' of vas cUlar bwl dles

(Plate I, D)-

Simple leaf

 

As the five bundles fornin; the trace to the single leaf pass
into the basal portion of tie pulvixius of the petiole, the two nenbers e
each lateral pair bBCOms united into one; tie xylen lies in the centera
with the phloem suri ound ing it. above this point,there is anastomosing
an1on3 the bundles, and they then been 9 reu11a13eo and form a circle of
tissue in tLe cezmte of the pulvinus} only a small pith retaining. at
the upper portion of the pulvinus, the pith increases in size, and the
ring of vascular tissue 3ra.lu11ly sepc rates into more or less distinct

bundles.

above the pulvinus,five bundles are distinct,.arranged in a

T"

circle wiich is open on the ventral side (Plate VIII, D, C). inere is a
medi.an dorsal bundle d)with two lateral ones on either side, 1, 2, 4, and
5.' The petiole in cross section at this point is round with a proove on
the ventral side. Ike flange or dn3 pr esesit on eiJhe or side of this
groove runs t7e fdll length of t?e petiole, up to the point of attachment
of .Le stipels.

Bundles l and 5, above the pa lVlnlS, send off small br3DCL
bundles, la and 5a, which form the s
the point where they pass out into the stipels at the base of the blade,
branch, one part forming the trace to the sti} el and the otler reuniting

with ti1e bundles l ard 5 frmn di a: they originally cane.

Two small bundles, 3a and 3b, consisting of only a fe" co: ducting

cells, branch from the ad; 'acent bundles a few millimeters above the pul-

vinus. At the base of the lads t1ese two bundles unite with the median

dorsal bundle and to to form the Lidrib of the blade.

above the attachment of the stipels Just below tLe blade, the
bundles of the petiole draw close together, and l, 2, and be become ad—
nate to each other. The sane union occurs with 5, 4, and 3b. Thus the

petiole at this point in cross section ias thCu apps srance of possessing

Ci“

a contracted, cres cent-sh1p e1 me 33 of conducting issue, actually drn-

sistin: of united bundles. As this enters the blade, bundle B’uuited

3a and 5b, form the midrib of the leaf blade toeeuher with a brancn

\-

l and 5. Bundles 2 and 4 soon separate from 1 and 5)and form the
lateral veins on either side of the midrib. The recain1n3 portion of l
and 5 fcrm the veins of tLe sim ple eaf which follow closely the K"3 iii
of the blade.

Sections of the nidrib at various places from the base of the
blade to tLe apex were studied to determine the forr:ation of the branch
veins. It was found that Whenever a vein branched from the midrib, a
small patch of xylem and leoen cells sc3drated from tlm 1.- idrib bundle.
Thus as the consecutive veins are fozrei, the amount of tissue in the

midrib decreases’until finally at the apex it consists of cm dy a fen

xylem and leoem.cells.

Beaten-Lilia:
1he coui se of t1e vascular tissue in tie pulvinus of the come
pound leaf is essentially the same as in that of the simple leaf, with
the exception that there are more bundles involved. In fact, except for
th greater number of bundles, the structure of the entire petiole up to
the point where the lateral leafl ets orL inn 1teJis sinilar to that of tne
sim3 le leaf (Plate VIII, F, d). lhus the nixe bundles 3lus the two

terall ones fonrinr the stipellar traces .pass upvard urc ~an'ei unti

-51..

just below the opposite lateral leaflets.

(0
cf
H
1e
(D

diVide, one-r alf passin3 into the

bundle. Just above

as some of then pass off as traces to

Bundles 2 and 8 of the petiole foam

five which pass into each lateral leaflet.
into tbrec parts, the middle portion of which
iole above the attachment of t1e leaflets.
leaflet forms part of the trace into it;

to tre at side, ulere it fonds per

The sare occurs in the case of bundle l.

divide into three parts,and behave as in

pairs of lateral bundles of

bundles derived from adjacent bundles of

ls and tite oth er reuniting

t 7123

t cf the trace to the

Here the traces to the stiyels

Wi th
°,there is a oprli-
rena ininsj- bundle s
lateral leaflets.
the median bundles of the
Bundles l and 9 each divide
passes upward into the pet-

Ihe branch nearest the one

the otl aroun

er branch passes
“ther leaflet.
Bundles 7 and 3 similarly each

the previous case. Thus the two

each trace to tie leaflets consists of two
the yet iole, and tm from bun-

dles from the other side. There is sore anestomosin; between bundles 3
wfl4,aui6ani7.

The five bundles making up each trace to tie lateral leaflets
reiain as a compac tissue in the center of the pe tiolule to tea leaflet
and do not appear as separate bundles as shown in the diagram.

Above the attachment of the leaflets)seven bundles continue,
arranjed in tte same winner as in the petiole below, although less in
number. “zeir further course is ol.flll r to tlat of the correspondinf
region of the petiole of the siluple leaf

Fleas:

 

The pedicel in cross section shows twelve vascular bundles’uhich
tend to be grouped in a circle, in four clusters of three bundles each
(Plate II, F). At the insertion of the pair of bracts which are attached
to the pedicel just below the calyx, one bundle on either side of the
pedicel divides, and the outer tarts pass through.the cortex and into the
bracts (Plate VII, C). Each trace at the base of the bract divides into
three bundles, which are the principle ones of the bract. r‘hus each bract
is furnished with a trace consisting of the larger part of a bundle of the
pedicel.
bi; e

as these traces pass into the bracts, ten bundles branch fncu

Tia

(I)

cular bundle in tie pediceIJand migrate into the cortex, tiers they
font a broken ring (Plate VII, D). It is these ten certiCal bundles
which furnish the vase dar supply of the calyx, corolla, and stamens. The
renaining bundles in the stele fonn the traces to the pistil. The
zygomorphy of the flower is noticeable from the first, for the vascular
an Cr/or'

supply to the peszefirar parts always passes from the stale before that to
Uhe a q ‘ .

m, anfer/or , . , r.

lne three pesserror bundles of tne ten in tne cortex, 1, a, and
10, the two lateral ones of which furnish the traces to the heel of the
corolla, have a somewhat different origin than the other seven. These
three are merely three branche from one bundle in the stale. The other
seven consist each of a single one. Therefore, the ten bundles areziot
exactly similar as to their origin.

The traces to the calyx and corolla bran h from the ten bundles

at practically the sane time. By referring to Plate VII, h, the origin

r-I P

of the traces to the united calyx can be followed. From five bundles,
la, 3a, 5a, 7a, and 9a, hree Shall bundles branch, and from the remain-
ing five which alternate with the first five, two bundles branch. These
two bundles unite with adjacent nerbers of the group of three. For

instance, la forms branches lb, lo, and ld- Bundle 0 hrs but tw

91‘
L

branches, 2c and 2d, and bundle 10a ferns 100 and 10d. In the base of
me calyx, ld unites with BC to fbrnxld, ac, and lb witfi 10 d to for: lOd

lb. lc ceitinues as a single bundle. In this gay)fifteen bundles pass

)

into tie calyx, thest beinf neio or less united at its base. Only a dis-

\L

tance of about ore hundred and twenty-five microns lies between the noints
from which the traces to the bracts pass.

alternating with the five bundles each of which sends tires
traces to the calyx, are the five, 2a, 4a, 6a, 8a, and 10a, which at the
sane time yinch off portions which form the traces to the corolla, 2b,
4b, 6b, 8b, and 10b. The remaining 10 bundles la, 2a, 3a, etc.)form the

lave nigrated to

lad

traces to the stamens. When the traces to the sepals
the outer portion of the cortex, a cleavage furrow begins in the cortex,

V

separating the corolla and the calyx from the pistil and the striais.

. . . an‘ferzor .. ,. .. . .. ,
This begins at the ,* .wi, r Side, noticeabl: zirst at the entaide of tne
two bundles which form the traces to the keel.

a little hiiher, the calyx is completely separated frat the
remaining floral parts (Plate VII, F , and it consists of a narrow circle
of parenchvma cells)about twelve cells in thickness. The two.mewbers of
the keel are separated iran the staminal ring, but the wings and the
standard are still united with it. The stanen traces, although they appear

to be arranged in a single whorl, actuall; are in two, those opyosite the

sepals aris 3 first and forming the outermost row and those alternating

with the sepals ari51ng later. The former bundles lie a little farther
toward the outside of he ring. The bundle of the stanen opposite the
standard, vhicb soon beccnes separated from the nine united ones, at this
state, is surrounded laterally by more cortica tissue then tEe other

steninal bundles.

The two win 3 soon are separated from the stm nir.al rinr leavin;

r".

the standard only attached to tie posterior stameu, which is now separated
from the remaining nine stamens. Then the standard and single stamen are
separated and all three outermost whorls are distii :zct (Plate "v I, G). Tee
vascular tissues in the stamens have an arphieribral arrangenent.

lbs traces to the pistil ccnsiet of tLe portions of the bundles
of the central stele tLich do not pass out as traces to tlie bracts and
to the otter three whorls of floral parts. These divide and foam a more

‘I

or less continuous circle in the stele. At the base of tne pistil, these
divide into tvelve bu;1les; six wove toward the posterior side and six
toward the anterior. Thus, by the time the pistil is sepa‘ated from the
steninal ring, the vascular supply consists of one large, cresceiit- shaped
bundle in the anterior side of the carpel, represent ng the dorsal suture
or midrib, and two posterior bundles at the ventral suture, equivalent to
the marginal veins of tie leaf whose margins can be seen meeting (Plate
VII F). These bundles, until the pistil separates frcn1 the staninal ring,
are adherent to the bundle of the siméle posterior stanen.

The ovules are attached to the placerts by the funiculus, and it

is throu;h this that the vas ulur tissue masses to the integuments, where

it brancLe 3 into W obundles- The two ventral lindle s of the ovary tLen

fir

—O\.I‘ -

' '- ‘. » r. r. .w “ I" 1 ‘ - -~ u H- 2- 'I
alternately {1V9 off traces to tne ovnle., as nelson (lfleil in: sTurn
(Plate II, 3). Tina the first ovule is eiyyliefi by tne bundle, the

second ovule by the other, etc. at the point wkere the lest ovule has

. .. til" 4n -, . .1. n .4-' . - -.,- 4: - , .. .3 _. j. .-.
been fornee, age vescsl42 i3snes Cuhulhd: into the btglfi arrange: in

+'- —. .. y 1 - , 4' TL 7 1p .‘ 4-». -
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lateral veins trenc ” free the nidrib of the leaf. Each of the ventral

bundles gives off only ew branches to the ovary well. These corres~

poni to the brancles of tile marginal veils of the leaf.

Pheseolns vul;gris 1. var. BlsCf Valentine is a dwarf been with

4-. ——...—.¢-—..-..;.

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same time, tFe first spire xylxn elegant: ejpegr. Loat of the r.atw1 e
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Literature Cited
COIL ton dObeI‘t 1;".
>
1912. A: investiéation of the seedling structur; in the
Leguminosae. Jour- Linn. Soc. 41: 33. Pl. 1-9.
run—— ——
De Defy, A- Trans latior.1 fro: tie GBTLEH 3y 5- 0- E'sei and D. H. “cott.
1884. Comrarative a: at,my of V e yhanorogags all the ferns.
i-xvi, l-QSQ. Illue. Oxfcxo- Claretdcn Ire 3
De Eolfi, Rudolgb.
1993. Beitraoe zur aretomischen C}.arekteris it der I: apoolcex.
Di as. LuLcnc and ffenhurq. (-7.. l r .
D:del , -1.
1e72. Der Uler.3n, das Dicotylefion 9:—dten:ele in die -fahl-
warssl. Jilitaoher fhr wisaenscraftliche totanik.
S. é3-193o I10 l“:o
Harris, J. Arthur. Sinno tt, Ldmund 3., ieniy 3.?er, John Yo, Durham, G-

Cf 1:13 _301: _af; vulraric. Jier. Jo;r. zot. EzoJ-1L3.
Fig. 1- 1‘3.
Jarvis, 3- b.
190 Arerican Varietlcfi 01 beans. Ceimell Lxr- Station rail.
260:143—223. 1 . ~15.
Tageli. Carl-
1553. Des dachstun do: Stagnes und fie: hurze I bei d3
,. \\ . o
eeiasspflanz n und die nno rilnan: dcr .efasctcrn'e 1;

. ‘I -. o ... I
stencel neitr';e zur ”issenscheftlicizc1 notanik.
3rstes Heft. 91—23. 3 fig. Le igzif Verlar von Wilhelm
Engelmenn.

I. 313011 , . ay.
1932 inVHot““tjoL€ in the “o.aic (iseaso of teen (Phaseolu:
val aria L.)- Lickiran aoric. TD- eta. Tee}. pull.
': I I — ~ ‘
llizl-Vl. Pl. l-l-.

1931. the va—sc ;ml r anatomy of d_im 1:33 aii trii-e ron;

 

 

 

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Anatomy of Thesiolus vx ifris L. var. Ll..-..c‘:—: .hlen’zine.
Plates I-III are {LOtOLlCPOfTiihu reduced L x. Plates IV-JII

dra r with camera lucida: reduced 4 x. Plate TIII reconstructed frou
transverse sectiege rawn wit; celera lucila; reiueei 4 x.
The followin“ abbreviat one re used: AL, aleurone; F, brect;

:- 1 j #3 -r\".' l K ‘ I"‘ ‘o I“ "F' A‘ I‘v“. "- w - "-‘n"
.JC, heal-33.; 0‘31; Ul Lezlf. l3, LEAHCL, .4: CC-‘rt‘JJ, ' LIA, CQAALIUQJ Ci“, Cleavvgge

v- ° 1 . -' .,1..--. n~ ,1‘ .. ~ 1. h -. *x' .7.

furro , cu, cutlclc, CA, CclJL, cu, cells orgy», J, dermatu e , uU, ucr-
. W L‘ ' 7 .‘~ vv I 3r" . o r.‘~v‘ ~- . -1 m. w . H. a 2:1 ‘.: 1- r‘ o --.

S“; can le of Ofurg, 1,, c: flcucl. :. .r, Gilgajmlo, -, llberu, :C,

fascicular cultiun; E'PE, “eric
cell; GL, leLdulLr heir: H 1001, d Lair; F, fuz.ica.lz1e; I 13, inter—
faecic;lur certiam; K, keel; L, tr;ce to corolla. stuncn, calyx; LT,
lee? trace; L PH, metepllcerg LA, Legerfle ' O. cvule; E, parencgyle;
rd, Lalisade cells; FED. pedicell oqndle;; xE, 1e: iC”C cc; }EI, “criclem;
PL, plerr a; PE, phloem; II, pith; I in, rrctevilocn; IR :5, grirery
1loem; EEO, .rccaLLiuL; PX, ETGEOI?134; ER X, prilur;r xylex; R C, root
cap; 9E0 ’h, seccnlarr Dth‘L; o, etcha; SEC X, secondary xylem; 3 n,
strairdt heir; SI, sieve plate; 3}, eronfy mesor} yll; ST, starch grain;

STA, standarc; 5T1, stipule trace; T, t LLizi‘sec; TB, trace to tract;

4.“ .— ‘ ~.-— .. T ‘ ‘j . ' - .. ,.' T ‘\ - 4. 4..-.” v, - '
peu30Lt111 “glen; L 31, urcer epluerzgs; L ‘. unlucd s elens, I Vulh;

.o “ + 0' ‘ 1.3 'x“ If "' r- h” n--'vl -~
4E,Ve are; ouucle or ovary; q. filflh; L, my CL.

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