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mutton OF mmm AND LIGHT mmm
T0 In}: TOP/ROOT RATIO IN IETTUC'E

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Ear the Degree of Master of
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\ Rat Lansing. Michigan,

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INTRODUCTION
m

'Ihe study of the effects of nutrient supply on
the ratio of tops to roots in plants is of much interest
to the horticulturist and considerable work has been done
in attempting to determine whether the desirable increase
in top/root ratio in a foliage crop or the desirable decrease
in top/root ratio in a root crop may be secured through
varying fertilizer treatments. I

'Ihe effects of variations in length of daily
ligxt period on top/root ratio and the reasons for these
effects are also of interest but much less work has been
done on this phase of the subject. Recent suggestions
of a practical use for artificial illumination in the
growing of plants have occasioned this phase of the work.

It is the aim of this paper to present data
in regard to the effects of various combinations of
fertilizer and light treatments on the distribution of
powth in tops and roots oflettuce and radish plants.

103900

WGF‘II'IZEBATURE
==============s

Several factors with regard to variations in
nutrient supply and their effects on the distribution of
growth in top and root have been stuiied in the past.

Sachs (19) showed that roots were shorter in
nutrient solutions of higxer concentrations. and Nobbe
(15) showed that this same factor caused them to be more
branched.

Moeller (13) found that more dilute nutrient
solutions caused a decrease in actual root weight and at
the same time caused a decrease of sixty percent in top/root
ratio below that found in plants grown in more concen-
trated nutrient solutions with which he worked.

Tucker and von Seelhorst. (24) and ‘lhiel (22)
found that there were relatively more roots in soils with
low moisture than in soils with high moisture, and also
that there were more roots in soils having a low fertility
than in those having higo fertility, while von Seelhorst
(20), working on rye. wheat, barley. peas. beans, and
field beets. concluded that with high fertility. root
systems were larger and descended more deeply into the
soil.

Livingston. (12) working with wheat. found
that increasing fertility by the use of stable manure

- 3 ..

caused an increase in root system due to an increase in
secondary and not in primary roots. He also found that
there was no increase in dry weight of roots in the
fertilizer treatments.

Polle (17) found root systems more branched
and with higuer absolute weight in unfertilized soil.

Harris (9) found that tops and roots of plants
grown in concentrated soil extract were geater in green
weigit, dry weight. and length. He also found that in-
creased moisture and fertilizer. both had a positive
effect on the ratio of tops to roots. Weights of roots
in the dryest sand used were about three times the weights
of tops attached to them. while in wet sand the tops and
roots were about equal in weight. Increase in ratio due
to fertilizer was caused chiefly by increase in actual
weiglt of tops. More concentrated nutrient solution was
found by Duley and Miller (5) to increase the ratio of
tops to roots in corn plants. 'lhey found that this ratio
increased as the plants grew older.

Brenchley and Jackson (2) state that of the
plants nutrients tried. sodium nitrate was most effective
in promoting root growth in barlqr and wheat plants.

'lhe effect of nitrates in solution was also studied by
Turner (25) who found that in corn and barley, top/root

-4-
ratios were increased as the concentrations of nitrates
in the solutions were increased.

Tufts (23) drew the conclusion from work on
nursery stock that pruning or cutting back of tops caused
a decrease in root development. However correct this
conclusion may be. the evidence which he presents to
substantiate his contention must be considered insuffic-
ient.for he quotes only coefficients of correlation
between tops and roots in proof of it. A high coef-
ficient of correlation between tops and roots of plants
which were unpruned and another high coefficient of cor-
relation between the tops and roots of the plants which
were pruned does not indicate that pruning decreased root
development, but sbmply indicates that within either one
of these lots. the top.growth nearly parallels root
growth. The coefficients of ccrrelation would still be
very high if the pruning had greatly increased root growth.
provided the weights of roots bore a rather constant
relationShip to the weights of the corresponding tops in
that particular lot of plants. However, Chandler (3)
gives figures to show that the dry weight of roots of
severely pruned apple trees was 49.5 percent below the dry
weight of roots of unpruned trees. 'Loomis (11). working
on vegetable crops, found that severe root pruning had no

permanent effect on the top/root ratio.

.. 5 -

It may be seen from the foregoing review of
literature that many workers have secured results which
are apparently contradictory to the results found by
other workers. In general. it may be said that no
consistently significant effects have been produced by
any practical fertilizer or cultural treatment.

Considerable data on the different effects of
artificial illumination and shortened day on the gowth
of plants are available but very little of it pertains
to the effects of varied length of daily light period on
the distribution of growth in top and root.

The first experiments with varied light periods
were those of Siemens (21) who found that electric light
produced much the same effect as sunligit on plants and _
concluded that it could be used a s supplementary illumination.

- Bailey, working with the electric light at
Comell. (1) showed that the light caused fifty percent
improvement in lettuce over the checks in three weeks time
after transplanting. He concluded that electric light
could be used to advantage in the forcing of some crops
as it caused better growth and earlier maturity. 'lhe
effect of lig1t on growth and earliness of lettuce was
also observed by Bane(18). He found that added light
caused some plants such as Spinach and endive to run

quickly to seed. while with the radishes. he'concluded

.. 5 -

that proper watering was more beneficial than improper
watering plus ligut. He worked with the incandescent
lamp and found it superior to the electric arc light.

The incandescent gas light was used by
Corbett. (4) He found the light caused earlier maturity
in lettuce. earlier blooming in tomatoes. and a himer
sugar content but loss of weigxt in roots in sugar beets.

Garner and Allard (6) worked on the effects
of vatied lengths of daily light period with special
reference to their effects on vegetative growth and the'
initiation of the reproductive processes in plants. They
found that sexual reproduction in plants would take place
only under favorable length of day. which might be a long
day or a short day. depending on the individual variety
of the plant. Other than favorable length of day caused
unfruitfulness. This was sometimes accompanied by unusual
vegetative growth while at other times it resulted in
dwarfism. They learned, too. that tuber formation in the
Irish potato proceeded much more rapidly with a daily
light period of ten hours than with light periods of either
five or thirteen hours. (7) They also found that long
day caused a higaer content of redming sugar in the plant.

Oakley and Westover (16) showed that the
effects of varied day lengths on seedlings of some varieties

of alfalfa were sufficiently different from the effects:

- 7 -

on other varieties to make it possible to identify
alfalfa varieties by simply growing them under varied
lengths of day and observing their behavior. Hightingale
(14) concluded that the effects of varied day lengths
were associated. in part at least. with the effects of
light on synthesis of nitrogenous compounds from soluble
nitrogen and the subsequent effect of this nitrogen on
carbohydrate utilization. A speeding up of the time of
blooming of Easter lilies was fOund by Hendricks and
Harvey (10) to be correlated with an increase in carbo-
hydrate content of the leaves when grown under continuous
artificial light. They found a specificity in light in-
tensities for blooming. which varied for different plants.

Working (26) found that light is a very
essential factor in the production of new roots of aspara-
bus and suggested that this may be due to a change in
the carbohydrate gradient due to photosynthesis.

The effects of light treatments on the top/root
ratio have not been studied very extensively for little‘ pub-
lished work on this phase of the subject could be found.
In all other cases of the study of factors affecting
top/root ratio. the actual individual ratios have not been
calculated. the ratio of the average weight of tops to

the average weight of roots having been used instead.

EXPLANATORY NOTES
W ====

 

All the plants in the following eXperiments were
grown in new six-inch pots. each pot being supplied with
drainage material and filled with loose ‘soil which was then
compacted slightly and watered. As soon as the plants
were set the pots were plunged in sand in a bench. care
being taken to distribute the treatments well throughout
the bench to eliminate place effects. In order to keep
soil moisture nearly constant. all watering was done with
a measure so that each pot received the same amount of
water. i

The radishes used in these eXperiments were
grown from seed furnished by Hofessor George E. Starr
and consisted of a strain of the Scarlet Globe. variety.
specially selected for uniformity in growth and type.

'lhe plants were grown in flats and carefully selected
when they were put into pots. The lettuce was grown from
seed secured from Mr. Yonker of Grand Rapids and the
variety was Grand Rapids Fcr cing. The seed was sown very
thickly in flats and the plants carefully selected when
they were pricked off into the bench. They were again
selected when they were potted.

 

 

 

 

 

L__ .‘_

-9-

In harvesting. the tops were cut off at the
ground surface and individual green weigits secured im-
mediately. Samples of the tops were taken for analysis
and moisture determination.

The roots were carefully washed out in water.
rinsed in clear water. and the excess moisture removed
by leaving them between sheets of paper for a short time.
The individual peen weights were then determined. care
being taken to record each root weigmt along with its
corresponding top. Samples of the roots were also taken
for chemical analysis and determination of the percentages
of moisture in each lot.

In all the data presented. the average green
weights of tops and roots in each of the lots are given
along with the probable errors of these averages. The
probable errors were computed by the formula: P. E. =
standard deviation times .6745, when the standard deviation
is $3 . (2d2 indicates the sum of the squares of the
individual deviations from the mean. and N stands for
the number of plants in that treatment.)

In all ”cases the ratio of top to root was cal-
culated for each plant separately and the average for each
lot is shown in the tables along with its probable error
as calculated by the formula Just described.

- 10 ..

It should be noted that in no piece of work
which has been published on this subject have the indiv-
idual ratios or average ratios been calculated. It has
always been taken for granted that the ratio of the
average weight of tops to the average weight of roots
was the same as the average ratio of tops to roots when
these ratios were calculated individually. These quan-
tities may or may not be eqtal. In other words.

'2; Z'H’R my or may 11°); equal 11- R . mese quotients

N
will vary very widely. especially when the absolute
ratios vary considerably along With rather wide variations
in actual weights of tops and roots. A single example

wilJl suffice to draw attention to this difference.

 

weight of Weigit of Na
tops roots calculated
individually
18 16 1.12
_19 ‘ _ _ .2 5.00
Average 1; 9 3.06

But 14/9 = 1.55
Here it is seen that the ratio of averages or

T

2T all]; is 1.55 while the average ratio. or Ella/3
is 3.06. Extreme variations have been chosen here in
order to accentuate the difference mueen average ratio
and the ratio of averages. but the fact remains that there
was not a case in the work done where these figures were

exactly coincident.

- ll -.

The following procedure was employed in the
analysis fcr carbohydrates.
Sampling.

The green material was immediately out up finely
with a knife and well mixed. A weigied beaker was filled
with this material and again weighed. This was placed in
an oven at 86° C. until the contents were thoroughly dry.
weigted again. and the dry material saved for analysis.
Grinding.

The dry material was ground in a mortar until
it would all pass through a 60-mesh screen. It was then
placed in 8-oz. bottles and heated in the oven to drive
. off hygroscopic moisture.

Preparation 3_f_ Extract.

(he gram of the oven dry material was placed
on a filter and washed six to eight times with successive
portions of cold distilled water. the filtrate being
caugut in a 250 cc. volumetric flask. The residue was
saved for starch analysis. The filtrate was clarified
with dry lead sub-acetate. made up to volume. filtered.
200 cc. of this filtrate was transferred to a 250 cc.
volumetric flask and de-leaded with dry sodium carbonate.
It was then made up to volume and filtered again and the

- 12 -

filtrate saved to furnish aliquots for sugars and for
hydrolysis in the determination of total sugars.
Egee-reducing sggars.

30 cc. of the GuSO4 solution. 30 cc. of the
alkaline tartrate solution. and 60 cc. of water were,
placed in.a beaker and brought to boiling. 25 cc. of the
water extract of the material'under examination were then
added and boiled two minutes. keeping the beaker covered
with a.watch glass. It was immediately filtered through
a prepared. dried. and weighed gooch crucible. using suc-
tion. The oxide on the filter was washed with.water at
60° C. and with a small quantity of alcohol. The gooch
crucible was then placed in an oven for thirty minutes.
cooled in a dessicator. and weighed. The quantity of
cuprous oxide was then determined and the equivalent quan-
tity of dextrose secured from Allihn's tables.

Total sugars.

50 cc. of the original sugar solution were
pipetted off into.a 100 cc. volumetric flask. neutralized
with HCl. and 5 cc. of concentrated H01 added. This flask
‘was then placed in a water bath at 60° C. and held there
for fifteen minutes. removed. cooled. neutralized. and
made up to volume. Determination of dextrose was made as

in the case of free-reducing sugars. using 25 cc. of this

solution.

- 13 -
Sucrose

The difference between total sugars and free-
reducing sugars gives the amount of sucrose.
Starch.

The filter paper. holding the sugar-free solid
residue. was punctured and the residue washed into a small
beaker. This was held on a,hot water bath for fifteen
minutes and the cmtents stirred constantly. cooled. a
solution containing .1 gram.of taka-diastase added. and
this solution incubated at 55° to 40° 0. for 24 hours.

It was then filtered into a 700 cc. Erlenmeyer flask. 8 cc.
of concentrated H01 added in sufficient water to bring the
volume up to about 150 cc. The flask was then connected
to a reflux condenser and heated for 2.5 hours. cooled.
neutralized with Ham. clarified with lead sub-acetate.
made up to 250 cc. volume and filtered. Iy200 cc. portion
of this filtrate was deleaded with 113200;. made up to
volume. and filtered again. Determination of dextrose

was made exactly the same as in the case of free-reducing
sugars. using a 25 co. aliquot of this solution.

Total polysaccharides .

 

A one-gram sample of the original dry material
was placed on a filter and the sugars removed by washing
several times with water at 30° to 40° c. The residue

was then washed into a 700 cc. flask and hydrolyzed with

H01 as in the case of starch determination. the clarif-

. - l4 -

ication and deleading processes. and the determination of
the amount of dextrose were identical with those employed
in the determination of starch, after the starch had been

hydrolyzed in a similar manner.

-15-
£££§§£E§EIAE
252;

WTI.
ma

Effects of Good and Poor Soils. and of Single and
Cumulative applications of Fertilizers
on Shoot/Root Ratio in Lettuce
and Radish.

Lettuce was sown broadcast in flats on October
14. 1924. pricked off on October 20. and transplanted into
pots on November 7. Radishes were sown on October 20 and
were potted on November 7. The radishes grown in poor
soil were sown December 15. 1924. and potted January 15.
1925. The lettuce was harvested February 9. 1925. The
first crop of radishes was harvested December 15. 1924
and the second crop on February 19. 1925.

Two kinds of soil were used in this experiment.
The good soil consisted of five parts of loam. thorougily
mixed with one part of coarse sand. The poor soil con-
sisted of five parts of coarse sand. mixed with one part
of loam.

The data secured are presented in Tables I and
II. It will be observed from the results shown in Table
I on lettuce. that lots 1. 5. and 7 have top/root ratios
which are apparently higier in the good soil than in the

poor soil. while in lots 5. 9. 11. and 13. the reverse is

- 15 ..
true. Since these effects of good and poor soils are
inconsistent and insignificant as determined by their
probable errors. no generalizations as to differences
in soils may be made.

In.comparing fertilizer treatments. the top/
root ratios in lots 15 and 14. both of which received
potassium fertilizer. are lower than in any other treat-
ment.of the series. This difference is significant. while
there are no significant differences among any of the
other treatments.

In every case shown.in.Table II. the ratio of
tops to roots in radishes is less in poor soil than in
good soil. but in no instance is this difference sign-
ificant. .

‘Lot we. 5. which was grown in good soil and
fertilized with potassium. had a top/root ratio which was
apparently lower than the tap/root ratios in any of the
other good soil treatments of this series. The same holds
true for the potassium treatment in poor soil. Lot no. 6.
Again. these differences cannot be relied upon as fUmnishihg
conclusiVe evidence of fertilizer effects since their

probable errors destroy their significance.

-17..

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-19..

mg;

Effects of the Time of Application
of Fertilizers on Swot/Root
Ratio in Lettuce.

 

Lettuce was sown broadcast in flats on January
22. 1925. pricked off February 2. and put into pots on
February 26. and was harvested April 22.

The soil used in this experiment consisted of
a mixture of one part of sand to two parts of loam. The
individual fertilizer treatments and the results secured
from them are shown in Table III.

ham the data given. the time of application
of fertilizers appears to have had no signfic iant effect
on the top/root ratio. When the probable errors are not

considered there appears to be a sligit increase in ratio

due to later applications of nitrogen. while later applic-

ations of phosphorus appear to cause a decrease in ratio.
but in no instance shown. are these increases or decreases

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- 21 H
EXPERIMENT III.
Effects of Variations in Daily Light

Period on moot/Root ratio in
Lettuce and Radish.

 

 

The plans for this experiment included a stuly
of the effects of full and cumulative applications of fer-
tilizers on lettuce. full applications of fertilizers on
radishes. and the effects of prolonged and shortened ligit
periods on both lettuce and radishes. ‘

Lettme was sown October 10. 1925. pricked off
October 17. potted November 5. and harvested January 4.
1926. Radishes were sown October 24, potted November 4.
and harvested December 15. 1925.

I In order to study the effects of extended and
of diortened ligxt periods. the following set-up of appar-
atus was employed. Three 1000-watt. 110 volt. nitrogen-r
filled incandescent electric lamps. covered by Benjamin
reflectors. were hung at a height of four feet two inches
above a bench. 5' x 21'. These lamps were approximately
1600 candle power each. They were lighted at dusk and
turned off automatically atll o'clock P. H. The plants
under these lamps were eXposed to light for a 15% hour
period each day. i

The plants in another series were given a short-

-22..

toned daylight period. These were covered at night with
beaverboard boxes. 8' long. 5' wide. and 5? high. These
boxes were painted black on the inside art! were fitted
with four 1" x 5" ligit-proof ventilation holes at each
end. They were lowered over the plants at 4:00 P. M. and
removed at 9:00 A. 11.. thus giving the plants seven hours
of ligit daily. After December 1. the boxes were set

on at 5:00 P. M. and taken off at 9:00 A. M” decreasing
the daily light period to six hours. The treatments with
the data secured on each are, shown in Tables IV and V.

It should be noted in Table IV. that‘in com-
parison of lots 1 and 6. neither receiving fertilizer but
lot 1 having a longer daylight period. the top weights
are practically equal. there being no sigiificant increase
due to the extra light. The decided increase in root
weigit'under long day causes an apparent decrease of the
top/root ratio from 4.12 in lot 6 to .80 in lot 1. but
this decrease is also insignficant. However. these wide.
though insignificant variations. may be indicative of some
significant variations which might be found to exist if
a sufficiently large number of plants were used so as to
materially reduce the probable errors.

The actual weight of tops is very greatly in-

creased by the addition of fertilizers but in all cases

 

- 23 ..

except in lot 5. the root increases so nearly parallel
the increases in tops that there are no significant
differences in ratios among the lots which received fer-
tilizers.

In lots 6 and 7 (Table IV). neither of which
received fertilizer. there is a decrease in top weight
under the short day. However. the tops under short day
plus fertilizer are larger than the tops of plants under
normal day or long day where no fertilizer was applied.

The results shown in Table V on radishes agree
quite consistently with the results on lettuce. so far as
Mat and fertilizers affect the top/root ratios. except
the comparatively low ratio in the lot having lorg day
and no fertilizer. lot 1. There are no significant diff-
erences in ratios due to fertilizers alone.

Potassium applied alone very materially decreased
top weigit of radishes as compared with lots receiving
nitrogen. but a slight decrease in roots paralleling these
decreases in tops destroyed the sigiificance of this
effect on the ratios.

It should be noted that the actual weigit of
tops of let nice plants under short day plus nitrogen is
practically equal to the weigit of tops of plants under
normal day.

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-25-

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.. 26 ..

The carbohydrate analyses of samples from some
of the lots of lettuce in this eXperiment are given in
Table VI. Samples for analysis were taken in the fore-
noon. Both tops and roots of plants grown under normal
day. lot 6. or long day. lots 1. 2. and 5. are fairly
high in all substances for which they were analyzed.
while the quantities of free-reducing sugars. total
sugars. sucrose. and starch were practically negligible
in the short day plants. The percentage of total poly-
saccharides in short day plants was very materially
reduced also. The actual quantities of total polysac-
charides in these plants were very much less than the
percentages in the table indicate. since the plants
themselves were very much smaller than the plants grown

under long day.

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-23-

MSCUSSION AND CONCLUSIONS
w nu: m

The value of any treatment used in plant culture
may depend not alone on the actual amount of growth which
it makes in a plant but also on the distribution of that
growth as regards top and root. It is very evident that
if some treatment were available which. when applied to
a crop of lettuce. would increase the top/root ratio by
increasing the growth of tops relative to the roots. this
treatment would be valuable to the lettuce grower. m the
other hand. if some treatment should cause the reverse
effect on a root crop. it too would be of practical import-
ance in vegetable growing.

Data presented in this paper indicate that under
the conditions of these experiments. fertilizers per se.
or the time of their application. or light treatments.
exert very little significant effect on the top/root ratio
in either a positive or negative direction. The nearest
approach to a significant effect is in the case of potash.
which in one case on lettuce. decreased the top/root ratio
sigxificantly and in all other cases where it was used.
decreases were indicated although mathematically insignf-
icant. The variations in the ratios due to the special

ligxt treatments. thougi apparently large. are found to be

- 29 -
unreliable when tested mathematically. They may be
indicative of real variations which would have existed if
the lots had contained a sufficient number of plants.

It is true that previous investigators have
reported changes in the top/root ratio which were accounted
real and used for drawing«conclusions. but the method used
generally in the determination of the ratios-~that of
using average weights of Shoots and roots and not the
average ratios with their probable errors-~would seem at
fault. rendering the results of doubtful value. Variations
in the relative weights of tops and roots and consequenfly
in the shoot/root ratios. when the plants are grown in
soil. are very great. even under the best controlled cone
ditions. Tbs conditions demand an application of the
most rigid mathematical tests. namely that of taking in-
dividual matched weights of tops and roots and from these

deriving the average ratios and their probable errors.

-30-

Data are presented which show that under the
conditions of these eXperiments. the top/root ratios
in lettuce and radish are comparatively constant fig-
ures so far as the effects of nutrients or their time
of application are concerned.

Prolonged and shortened light periods pro-
duced apparent effects on top/root ratio but these
effects were found to be insiglificant when tested
mathmetical 1y .

WW1?)

 

The writer is deeply indebted to Dr. John
W. Grist whose kindly help and skillful direction have
made this work possible. and to Professor V. R. Gardner

for reviewing and criticizing the manuscript.

LITEBATURE CITED

 

 

 

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- 33 -

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