A PLAN
FOR COOPERATIVE RESEARCH
ON THE SALT REQUIREMENTS

OF

REPRESENTATIVE AGRICULTURAL
PLANTS

Prepared for a Special Committee

OF THE

Division of Biology and Agriculture

OF THE

National Research Council

EDITED BY

BURTON E. LIVINGSTON

DR. A. G. McCALL,

LABORATORY FOR SOIL INVESTIGATIONS,

un;v?=f?s!ty of M^RVLANP,

, . M t'GE PARK. MD.

SECOND EDITION

BALTIMOKB
1919

A PLAN
FOR COOPERATIVE RESEARCH
ON THE SALT_^REQUIREMENTS

OF

REPRESENTATIVE AGRICULTURAL PLANTS

PREPARED FOR A SPECIAL COMMITTEE

OF THE

DIVISION OF BIOLOGY AND AGRICULTURE

OF THE

NATIONAL RESEARCH COUNCIL

EDITED BY

BURTON E. LIVINGSTON

SECOND EDITION

Baltimore

\2s

Vv\

THE FIRST EDITION OF THIS PLAN
WAS MIMEOGRAPHED, AND A HUN-
DRED COPIES WERE CIRCULATED. THIS
SECOND EDITION IS ESSENTIALLY
THE SAME IN CONTENT AS THE FIRST.

HBAM UBR*«V^GftICLa.TUWt:

PREFACE

During the war period the Division of Agriculture, Botany
and Zoology of the National Research Council established a spe-
cial committee to attempt the organization of a nation-wide co-
operation among the research scientists interested in plant nutri-
tion. The project is of fundamental importance, and is to be
continued under the new Council. The purpose of this coopera-
tion is to hasten the acquisition of definite knowledge regarding
the salt requirements of a few representative agricultural plants,
and it is hoped thus to accomplish in a small number of years
what would usually require many decades. Experimenters are
earnestly requested to further this work in every way possible,
and it is hoped that at least part of the time of one research
worker in each laboratory where this kind of work is carried on
may be devoted to this project. If all of the time of one or more
persons can be devoted to the work, of course, that would be still
better for the progress of knowledge in this field.

The need for some well-established, correlated, quantitative
knowledge of the salt nutrition of plants is clearly appreciated
by all students of this important subject, as is also the present
almost total lack of such knowledge. Our theories are incomplete
and vague, and the experimentation on which they rest has not
generally been such as to allow correlation between the different
pieces of work. - It is planned that the present cooperation by a
large number of experimenters will soon furnish a great body
of correlated information regarding the salt requirements of the
plants studied ; all workers in the project are urged to follow
the methods described on the pages following this preface, to
the end that all results obtained may be as truly comparable as
possible. While each cooperator will of course be perfectly free
to interpret and publish his results as he may see fit, the com-
mittee hopes to be able to bring all the contributions together
from time to time as the work progresses, so as to build up
rapidly a rather complete statement of the salt requirements of
each plant that is included in the, scheme.

It is clear that this project is a physiological one, and that the
results obtained cannot be expected to furnish direct and imme-
diate information as to the fertilizer requirements of these plants
when grown on any agricultural soil ; each soil offers its own set

451805

of prob1errtS'-^.o the agronomist, as does also each climate and
each plant form. But it seems safe to predict that the correlated
system of physiological knowledge that is to result from this
cooperation will place in the hands of agronomists and agricul-
tural chemists many valuable facts and principles. Upon these,
with further experimentation in the field, may be built up a
greatly improved system of fertilizer practice and crop rotation.
The present project is therefore fundamental to the rational
advance of agricultural science and practice.

The shortage of potassium in this country during war time
emphasized the need that our knowledge of the best ways of
using fertilizer salts in general should be increased and put on
a definite basis as rapidly as possible. This, together with the
high price of nitrogen-bearing fertilizer material, gave to this
project some of the characteristics of a war-emergency problem,
but the problem is exceedingly important and fundamental to
agricultural development in general. A concentrated effort
toward the building up of a reliable body of American scientific
results in this field may be regarded as higjily desirable from the
standpoint of national welfare. Also, the fact of cooperation
itself should benefit American science very greatly, and it may
be hoped that this general method of advancing knowledge may
eventually become much more common among democratic peoples
than has been the case in the past. Aside from war-emergency
matters, this is one of the aims set forth by the President of the
United States in his executive order establishing the National
Research Council on a permanent basis.

This project itself contemplates only physiological studies, car-
ried on with water and sand cultures, thus avoiding many of
the complications introduced when agricultural soils are in-
volved. Besides determining as precisely as possible what are
the most favorable total concentrations and sets of salt propor-
tions for the various developmental phases of the plants studied,
it, is planned to include experimental studies of the relative de-
grees of^susceptibility to fungus attack Exhibited by the cultures
in different solutions. It is also planned to obtain chemical
analyses of the plants grown and to correlate these results with
the characteristics of the nutrient media used.

The problem for any single plant is so complicated in itself,
and the amount of logically planned and carefully carried-out
experimentation required (before even tentative conclusions may
be attained) is so great, that it seemed absolutely necessary at
the start and for the present to restrict attention to a very few

forms of plants. The work has been begun with the "Marquis"
variety of spring wheat, and an attempt will be made to advance
our knowldege of the salt requirements of this plant as rapidly
as possible. As a second plant, soy bean is to be employed, and
work upon it may be begun immediately if workers prefer to
deal with this plant rather than with wheat. In the beginning
the cooperation is to be limited to these two plants. Other plants
may be taken up when plans and methods have been perfected
and when the work may be well enough in hand so that the co-
operators may afford to leave the two plants just mentioned.
All of the wheat and soy bean seed used will be supplied by this
committee, so that all experimenters may be considered as deal-
ing with the same complexes of internal conditions as these are
presented in the resting seed. Arrangements have been made
by which the salts employed by all cooperators may also be of
the same lots. The standardized methods to be employed in the
beginning, as outlined below, are based on those of Schreiner
and Skinner, Tottingham, Shive, McCall, and Hibbard. For some
references to the literature in this connection, see the list of
citations following this preface.

Cooperators are asked to furnish the special committee with
data, as the work progresses, and generally to keep the committee
in touch with their work. It is of course understood that the
committee will give proper publicity to the work, with due credit
to all cooperators.

It is estimated that the materials and apparatus required by
one worker for a year will not cost more than $300.00, supposing
that some greenhouse space is available for winter work. Much
of the needed apparatus is generally at hand in laboratories
where studies in plant physiology are carried on.

Those who receive copies of this Plan are urged to look over
the outline of the project, and let the chairman of the committee
have their decisions at an early date, as to what they may be able
to do in this cooperation.* It is desirable to have as large a
representation as possible and it is hoped that many workers may
feel that this is their project, and that they will do all they can
to further it. The work falls readily into numerous sections of
different magnitudes, so that a cooperator may devote only a
small portion of his time to it and still obtain valuable results
toward the general solution of the problem. For example, if a

* Correspondence should be addressed to Dr. B. E. Livingston, Labora-
tory of Plant Physiology, The Johns Hopkins Unli><^^^rsi!ty,(^aMij®3C<leLjVId.

lI^boratory por soil investigations,

^UNIVERSITY OF MARYLAND,
COLLEGE PARK, MD.

worker might devote only an hour or two each day to these
experiments, the committee would be able to aid him in selecting
a small number of solutions for comparison. Every little piece
of careful experimentation (provided only that it fits in as a part
of the general plan) will count in the general summation.

K. F. Kellerman,

Wm. Crocker,

B. E. Livingston (Chairman),

Special Committee on Salt Requirements
of Representative Agricultural Plants,
National Research Council, Division of
Biology and Agriculture.
DR. A. G. McCALL,
ARORATORY POR SOIL INVESTIGATIONS,
''NIVERSITY OF MARYLAND,
■ ^ ' ^''■'^ IMRK, MD.

REFERENCES TO SOME PAPERS DESCRIBING METHODS

ON WHICH THE PLAN FOR THIS

PROJECT IS BASED.*

1910. Schreiner, O., and J. J. Skinner.

Ratio of phosphate, nitrate and potassium on absorption and
groAvth. Bot. Gaz. 50: 1-30. 1910. Idem. Some effects of a
harmful organic soil constituent. U. S. Dept. Agric. Bur. Soils
Bull. 70. 1910.

1914. Tottingham, W. E.

A quantitative chemical and physiological study of nutrient
solutions for plant cultures. Physiol. Res. 1 : 133-245. 1914.

1915. Shive, J. W.

A study of physiological balance in nutrient media. Physiol.
Res. 1 : 327-397. 1915.

1916. McCall, A. G.

The physiological balance of nutrient solutions for plants in
sand cultures. Soil Sci. 2: 207-253. 1916. Idem. The physio-
logical requirements of wheat and soy beans growing in sand
media. Proc. Soc. Prom. Agric. Sci. 1916: 46-59. 1916.

1917. Hibbard, R. P.

Physiological balance in the soil solution. Michigan Agric.
Exp. Sta. Techn. Bull. 40. 1917.

Shive, J. W.

A study of physiological balance for buckwheat grown in
three-salt solutions. New Jersey Agric. Exp. Sta. Bull. 319.
1917.

1918. Livingston, B. E., and W. E. Tottingham.

A new three-salt nutrient solution for plant cultures. Amer.
Jour. Bot. 5: 337-346. 1918.

*'0f course a large number of papers might be mentioned in this list, as
bearing in one way or another upon this project. From the point of view
of the logical analysis of the problem the papers cited heFe will be specially
valuable, and "numerous other literature references may be obtained from
them. Tottingham's bibliography will be found very useful in connection
with the general proposition of controlled chemical environment as far as
the root system of the plant is concerned.

McCall, A. G., and P. E. Richards.

Mineral food requirements of the wheat plant at different
stages of its development. Jour. Amer. Soc. Agron, 10: 127-134.
1918.

Shive, J. W., and W. H. Martin.

A comparison of salt requirements for young and for mature
buckwheat plants in water cultures and sand cultures. Amer.
Jour. Bot. 5: 186-191. 1918. Idem. A comparative study of
salt requirements for young and for mature buckwheat plants in
solution cultures. Jour. Agric. Res. 14: 115-175. 1918.

Schreiner, O., and J. J. Skinner.

The triangle system for fertilizer experiments. Jour. Amer.
Soc. Agron. lO: 225-246. 1918.

INTRODUCTION.

This project aims to test a large number of combinations of the
necessary chemical elements, to find out what combinations give
the most satisfactory growth of the plants considered. Different
phases of the development of the plants are to be treated sepa-
rately, to bring out any changes in the •nutritional requirements
that may supervene as gi*owth proceeds. As many different com-
plexes of climatic conditions as are practicable are to be tested,
to find out in how far the salt requirements may depend upon
climatic conditions. It is planned to find out just what sets of ^
salt conditions give the best growth for each type of climatic
complex.

The project thus contemplates a very thorough experimental
study of the physiological possibilities of the plants dealt with.
Just as the atomic weights of the chemical elements need to be
known with considerable precision before their relations to their
surroundings may be satisfactorily studied, so the physiological
characteristics of agricultural plants need to be known before
scientific agriculture may progress very far.

The cooperative feature of the project aims to secure a large
body of comparable data as rapidly as possible. A large number
of research workers acting simultaneously will be able to test
the numerous possibilities in a comparatively short time, and the
fact that all employ the same standard methods should make all
of the results fit into one general whole.

The following outline, which is planned to be extended and
improved later, has been elaborated through consultation with
a large number of specialists in this sort of work. It is hoped
that the essentials of the method here described will be followed,
since likeness of method is the prime consideration in work of
this sort. When alterations of the plan seem necessary the other
cooperators should be informed and an agreement reached
through the committee. Correspondence regarding the work
should be addressed to Dr. B. E. Livingston, Laboratory of Plant
Physiology, the Johns Hopkins University, Baltimore, Md.

DR. A. G.'McCALL,

THE PLAisA^WJOgi^ H^SeM"- investigations,

UNIVERSITY OF MARYLAND
The first and most important plant for the present purpo'se is

wheat, and a supply of seed of the ":fe^'rli&'S^ ^?fkj^% spring

wheat was obtained by purchase from Professor Leith, of the

Wisconsin Agricultural Experiment Station. Cooperators will

receive seed from Baltimore, upon request. A new supply will
be available in the fall of 1919.

The second plant to be studied is soy bean, and a supply of seed
has been made available through the kindness of Mr. J. E.
Metzger of the Maryland Agricultural Experiment Station. This
seed may also be obtained from Baltimore, on request.

TWO METHODS OF CULTURE.

It is planned to carry out this elaborate series of physiological
tests with both water and sand cultures, but it seems desirable to
press forward somewhat more rapidly with the former; most
workers may prefer to attack the water cultures first, since the
operations are simpler here. Both methods are set forth below.
Special details for soy bean and for the later phases of wheat
are still to be elaborated and modifications of the outline here
given may be required as the work progresses.

WATER CULTURE OF WHEAT.
Four Developmental Phases.

The development of the plant will be considered in four sepa-
rate stages or phases, three of these being defined by the degree
of development attained and the other by time duration. These
phases are as follows:

1. Germination Phase, from beginning of soaking till the
shoot is four centimeters high, measured from the seed to the tip
of the shoot.

2. Seedling Phase, from the end of phase 1 for a period of
five iveeks, without regard to the size of the plant.

3. Vegetative Phase, from the end of phase 2 until the first
appearance of flowering in the controls. [Controls are always in
Shive's best solution for wheat seedlings, IR5C2, by 1/10-incre-
ments (1.75 atm.) ; see below.]

Jf. Reproductive Phase, from the end of phase 3 until ma-
turity is reached by the best five cultures of the group of 20 or 21.

These phases ghould be adhered to with care, in order that all
the parts of the work may be comparable. It may be that their
definition will require alteration after the work is well in hand,
but the definitions here given will serve for the beginning.

It is aimed first to find out what four solutions should be
consecutively used to produce plants that are the best at the ends
of all four stages of development. Thus, after the plan has been
carried out we should be able to say that phase 1 should have

10

solution a; phase 2, solution b; phase 3, solution c; and phase 4,
solution d. Many other possibilities are clearly in the prospect,
but this plan appears to be best for the first study. It is not at
all well known how the solution requirements for best growth
may alter from one developmental phase to the next succeeding
one, nor is it known what may be the most satisfactory method
of dividing the growth period into partial periods to represent
the phases. The scheme of employing these four phases and
attempting to find the best solutions for each phase (the preced-
ing phase or phases having had their own best solutions) is
simple and readily practicable for making a start..

1. Germination Phase.

General Treatment of Seed. The supply of seed should be
stored in a, loosely closed container, with some access of air, and
in a dry, cool place, free from laboratory gases, etc. The seed
to be used in any test should be inspected, and obviously imper-
fect or otherwise apparently undesirable seeds should be dis-
carded. Soak ten times as many seeds as the number of seedlings
needed, for five or six hours in a glass vessel, with a volume of
germination solution equal to twice their apparent volume. Then
place them on the germination net.

The seeds should be uniformly distributed over the germina-
tion net. Since excretion and absorption by the seeds on the
germinating net tend to alter the germinating solution, care
should be taken that the seeds are not too crowded on the net.
Germination is to be continued until the shoots reach a height of
four centimeters, measured from the seed. A uniform series of
seedlings is then to be selected and placed in the culture jars. The
treatments for the four phases for wheat will now be presented.
Later modifications may be required, especially for the last two
phases.

Germination Apparatus and Method. For germinating the
seeds the following scheme is to be followed, at least in its essen-
tials. This is not necessarily the best plan conceivable, but it is
one fairly good way, and it is thought to be well adapted to the
various exigencies of a large number of laboratories and work-
ers. Uniformity of method among the various cooperators is
again to be emphasized here as absolutely requsite. Failure to
adhere to the standard method would effectually prevent the
different sets of results from being comparable. If modifications
are planned, the committee should be informed in this regard.

11

The germination net consists of ordinary mosquito netting,
thoroughly paraffined by dipping in melted "Parawax" (or other
paraffin of equally high melting point) . The net is to be tied
as tightly as possible over the top of the germination jar. A
new net should be used for each germination.

The germination jar is an ordinary 5-gallon stoneware jar,
approximately 28 cm, in inside diameter and 34 cm. high, glazed
inside and out. The germination net should be tied tightly over
the opening of the jar, so that when the jar is filled with solution
the water surface practically coincides with the plane of the net.

Insert in the jar a vertical glass tube, which will lie close to
the jar wall and project a few centimeters above the net, through
which it passes. This tube should be broken obliquely at its
lower end, where it rests on bottom of jar. The upper end should
be cut squarely off. The bore of the tube should be about a cen-
timeter, or more. New solution is added through this tube, so
as to be introduced at bottom of jar.

From a suitable support above, a glass thermometer is to be
suspended vertically, so that its bulb lies just entirely below the
net, extending through the latter at its center. This shows the
temperature of the solution that lies about the seeds.

It is aimed to maintain the temperature for germination
within about 2° C, and it will therefore be necessary generally
to place the whole jar in a larger water-bath, to which cold or
warm water may be added two or three times a day, according
to the needs of the temperature control. A better form of con-
trol may of course be used ; this method "by hand" is taken as
the simplest and least expensive. An ordinary galvanized iron,
wooden or fiber wash-tub is suitable for the bath in which the
germination jar stands. The bath water should not reach as
high as the edge of the netting where the latter projects over
the edge of the jar.

The apparatus should stand in a lighted place, subject to the
ordinary fluctuation of day and night, free from poison gases and
laboratory fumes, but should not receive- direct sunshine at any
time. It should be so placed that the overflow will be drained
away. Ordinary water is used for the bath; nutrient solution
for the jar. Solution is added to the jar once a day during
germination, and water is added to the bath as frequently as may
be necessary to obtain the needed temperature control. In both
cases there will of course be an overflow, the water solution from
the jar rising through the net and passing over into the tub.

12

The jar is filled at the start with the solution to be used and
two liters of new solution is added once each day, by means of
a siphon or funnel, the new solution entering through the glass
tube above mentioned. The same kind of solution is to be used
throughout the germination period.

Tests on the relation of the nature of the solution and its tem-
perature to rapidity of germination in the wheat to be employed
have been carried out at Baltimore, and one of the best tempera-
tures and sets of salt proportions for this wheat has proved to be
25° C. and Shive's solution R5C2 (0.175 atm.). The germina-
tion temperature is to be maintained at from 24° to 26° C, and
the solution to be used is Shive's R5C2; in 1/10 "optimal" total
concentration (osmotic value about 0.175 atm.). This solution
has the following volume-molecular partial concentrations of
the three salts; KH^POs 0.0018 mol.; Ca(NOOs 0.00052 mol. ;
MgSOs 0.0015 mol. No ferric phosphate is to be used in the solu-
tion for the germination phase of growth. This solution may
safely be prepared, for stock, thirty times as concentrated as is
required, so that 67 cc. of the stock solution plus two liters of
water will give a rather close approximation to the needed germi-
nation solution.

This stock solution from which the germination solution is to
be prepared by dilution (and from which the control solution
for later phases of growth is also to be prepared, with the addi-
tion of FePO< in that case) thus has the following volume-
molecular partial concentrations of the three salts (these values
being thirty times the corresponding values given above) ; —
K&POs 0.054 mol.; Ca(NOOs 0.0156 mol.; MgSOs 0.045 mol.
To prepare the two liters of germination solution required daily,
add 67 cc. of this stock solution to two liters of water. The
"error" is negligible and this quick method conserves time.

The seedlings to be, placed in the culture jars for the seedling
phase are to be selected for uniformity as to height (4 cm.) and
general appearance. Since ten times as many seeds are to be
placed on the net as are to be needed after germination, this
selection should be as satisfactory as is possible with present
knowledge.

It is convenient to select at once all the seedlings to be used
(and some extra ones), lifting them from the germination net
with care not to injure the roots nor to bring them into even
momentary contact with the hands, table, etc. The seedlings
thus selected are placed in one or more glass pans with germina-
tion solution 2 cm. deep, so that the roots are in the solution and

13

the shoots project above its surface. Then they are taken from
these pans, one by one, and fixed in the prepared cork stoppers.
They should not be placed in distilled water or tap water at all,
but are thus kept in the germination solution until they are
actually placed in the culture jars. Have the hands clean ;
paraffined forceps are useful.

2. Seedling Phase.

Culture Jars and Corks, and the Setting Up of Cultures. The
culture jars used for the seedling phase are to be ordinarily glass
fruit jars, of the "Mason" type, the quart size. It is essential
only that the capacity be approximately correct and that the
opening be suitable for the corks carrying the seedlings. One
distinct advantage of the "Mason" jar is that it is supplied in
three sizes (pint, quart and two-quart) , all with the same size of
opening; another advantage is that this jar is procurable prac-
tically everywhere in the United States, and at a low price.
The tops supplied with the jars are not needed in this work.

Each jar is to be covered by a cylindrical jacket of opaque
paper, white on the outside, to keep strong light from reaching
the roots of the plants. It is desirable that the jacket be so
arranged that it can be readily removed without disturbing the
plants (for examination of the root systems, etc.). A good
method is that employed by Shive (1915) . A jacket that is dark-
colored on the outside is not suitable, since absorption of radiant
energy is undesirable.

The corks used for closing the jars and for supporting the
seedlings should be of good quality, of the flat form, one-half
inch thick and of a diameter to fit the opening of the jar used.
They are to be thoroughly impregnated and thinly coated with
paraflfin, such as "Parawax." A very excellent arrangement for
mounting the seedlings is that adopted by Tottingham (1914).
Only five seedlings per jar will be used in the present coopera-
tion. It is strongly urged that this arrangement be employed,
for the sake of uniformity, but if another arrangement is used it
should conform in the essentials. Those essentials are : that the
five seedlings must be firmly held just above the seed in each
case, with but slight pressure opposed to subsequent increase in
the stem diameter in this region; that the jar be practically
closed; that the stopper be protected from fungi; and that the
technique of placing the seedlings be simple (so as to be rapid
and to avoid undue disturbance of the delicate plantlets during
the process of placing) . Ready-prepared corks may be obtained

14

from the committee at cost, — perforated ones $4.00 per hundred,
plain ones $3.50 per hundred. Corks require reparaffining from
time to time if they show fungus growth. The same corks are to
be used for later growth phases.

A good quality of ordinary cotton (batting) is best for fixing
the seedlings in the corks; absorbent cotton is not desirable (it
absorbs water much more readily than ordinary cotton) . Use
just enough cotton to hold the seedling securely in position, so
that it will not slip downward. The cotton will become com-
pressed, as the stem enlarges. The cotton is to be kept dry.

Jars should be thoroughly washed, rinsed in distilled water,
and dried (or each finally rinsed with the solution to be used
therein) before using. Each is filled to a point 1 cm. below the
lower surface of the cork. A non-perforated, paraffined cork is
inserted (to reduce evaporation and other changes during the
interim) and the jar is clearly marked with its solution number
(wax pencil). When all the jars of a series are thus filled and
marked, the work of placing the seedlings is taken up, the cork
bearing the five seedlings now replacing the non-perforated cork
that previously stoppered the jar. After each jar is supplied
with seedlings its jacket is put in place. The jacket should also
bear the number of the solution contained in its jar (marked in
pencil) .

The seedlings should be kept from direct sunlight and from
laboratory gases or other disturbing influences throughout the
process of changing from germination apparatus to jars, and the
series of jars is to be placed in the experiment location as soon
as all are ready. It is desirable that the placing of all the seed-
lings for any comparable series be completed as rapidly as pos-
sible, on the same day; the jars may be supplied with their solu-
tions on the preceding day, but are then to be kept stoppered,
as described above.

Any series may be set up either as a simple series or in dupli-
cate, triplicate, etc., according to the number of cultures in-
cluded, the time at the disposal of the experimenter, etc. In all
cases the control culture should be in triplicate; i. e., three cul-
tures in solution IR5C2 (1/10-increments, 1.75 atm.) are to be
included in every series.

Renewal of Solutions, and Observations During the Five-Week
Period of the Seedling Phase. The solution of each culture is to
be renewed every 31/2 days (nine renewals in the five- week
period). Details regarding the renewals are given below, also

16

regarding the preparation of the solutions, the experiment loca-
tion and exposure, and the records of aerial conditions.

Records are to be kept of visual observations made at the times
the solutions are renewed, regarding differences that may be
manifest among the various cultures. Attention should be given
to the root systems as well as to the tops of the plants. It is pos-
sible that a culture showing the apparently most vigorous plants
of a series at the end of the third week, for example, may not
show the most vigorous plants at the end of the fifth week, etc.,
and these records of visual observation are planned to bring out
such occurrences. Without such records important features may
escape notice entirely. (On comparing cultures, etc., when meas-
urements cannot be employed, see: — Free, E. E. Plant World
18:249-256. 1915.

Plant Measurements at End of Five-Week Period. At the end
of the seedling phase the following plant measurements are to be
made : —

(1) Length of longest and shortest top in each culture, meas-
ured from the seed (or the position where it was attached) to the
extreme tip of the plant.

(2) Fresh weight of tops for each culture as a whole. Cut off
each main root at its junction with the stem and consider all
that remains as the top of the plant. Cut tops into pieces as
much as is necessary, and immediately place all tops from each
single culture in a weighed test-tube, stoppering with rubber or
paraffined cork stopper. Stopper is removed when weighing
occurs. Weigh as soon as possible, and record fresh weight of
tops for each culture as a whole. Calculate this value to repre-
sent 5 plants in every case where the entire 5 plants are not
available.

(3) Dry weight of tops for each culture as a whole. After
fresh weight has been obtained, dry the tops, at a lower tempera-
ture first and then at 102° C, and determine dry weight. It is
well to place tubes in a desiccator on removal from drying oven
and to stopper each tube as it is weighed, using the same
weighed rubber or paraffined cork stopper for all tubes; this
avoids having a large number of weighed stoppers. Of course
other weighing vessels, etc., may be used ; the method above sug-
gested seems adequate and is simple and inexpensive.

(4) Dry weight of roots for each culture as a whole. Place
all root systems from single culture together and press gently
between sheets of blotting paper to remove most of the liquid.

16

Then dry in weighed test-tube, as for tops, and obtain the dry
weight of roots. Other suitable methods may of course be used.

(5) Dry weight of entire plants for each culture as a whole.
This datum is simply the sum of the corresponding dry weights
of tops and roots.

(6) Record any differences that may be manifest, but not
measurable in the above terms. Of course these observations
are to be made before plants are removed from the jar and stop-
per, and the whole manipulation of getting the above measure-
ments is to be carried out so as to prevent appreciable changes in
fresh weight before this is measured. Treat each culture sepa-
rately till its tops are in the stoppered tube, then proceed to next
culture. Preserve the dry material in envelopes, properly
marked, so that a reweighing or other future examination may
be made if desirable.

3. Vegetative Phase.

Preparation of the Plants. Germination is to be carried out
as for the seedling phase, and twice as many jars are to be set
up for the seedling phase as will be needed for the vegetative
phase. These cultures are to be carried through the seedling
phase in the manner described for that phase, but all cul-
tures ARE TO BE SUPPLIED WITH THE SAME SOLUTION, which

is the one previously found to be best for the seedling phase.
At the end of the five-week period there should be twice as
many plants, all nearly alike, as are to be needed for the
vegetative phase. Select five or ten plants from this lot to
represent the average, and record for them the final measure-
ments of the seedling phase, as stated above. From the remain-
ing plants select a uniform lot for the vegetative phase. It will
generally not be necessary to remove plants from their corks;
the cork and its plants will simply continue in one of the cultures
of the vegetative phase. All cultures are of course left in the
solution used for the seedling phase until transferred to the par-
ticular solution to be used for that culture in the vegetative
phase. Plants that are not needed are to be discarded after the
series for the vegetative phase is entirely set up. Of course,
duplicate, triplicate, etc., cultures may be employed; and tripli-
cate control is to be included, as in the seedling phase.

Treatment During the Vegetative Phase. All the different
solutions (see below) are to be tested for the vegetative phase,
to find out what solution is best for this phase, as will have been
done for the seedling phase. The procedure is the same as for

17

the seedling phase, with solutions renewed twice per week. It
may be necessary to furnish the plants with mechanical support.
The basis of the support should be a cylindrical wooden stake
(1/4 -inch dowel is good) and care should be exercised that the
leaves are not seriously crowded. The support described by
Hibbard (1917) is one satisfactory form. The stake is set in the
center of the cork in which the plants are arranged. This phase
ends when flowers appear in the controls, but this statement may
require modification as the work progresses.

Plant Measurements at End of Vegetative Period. These are to.,
be the same as those made at end of seedling period. Of course
visual observations on the plants are to be made from time to
time through the vegetative period, just as in the case of the
seedling period. Especially should the final records show obser-
vations on differences in inflorescence, for those cultures that
show flowers.

4. Reproductive Phase.

Preparation of the Plants. Germination is to be carried out
as for earlier phases and twice as many jars are to be set up for
the seedling phase as will be needed for the reproductive phase.
These cultures are all to be carried through the seedling phase
(with the best solution for that phase) just as in preparation
for the vegetative phase. Then a selection of one or two repre-
sentative cultures is made, for records of plant measurements
of the seedling phase, and the remainder are carried through the
ve.getative phase, but all with the ^ame solution, which
has been found to be best for that phase. At the end of
the vegetative phase one or two cultures are selected to repre-
sent the average, records are made of plant measurements from
these for the vegetative phase, and the remainder furnish the
selection for the reproductive phase. This selection is made just
as in the case of the vegetative phase described above. The
series may of course be in duplicate, etc. ; and triplicate control
is introduced as in earlier phases.

Treatment During the Reproductive Phase. -All of the solu-
tions (see below) are to be tested for the reproductive phase.
The procedure is the same as for the two preceding phases, with
renewal of solutions twice per week. The plants will probably
need mechanical support. This phase continues till maturity is
reached by the best plants of the series. The exact criteria to be
used may receive more attention as the work proceeds; it is of
course aimed to find out what set of salt proportions is best for

18

the reproductive phase, when the plants have previously been
supplied with the respectively best solutions for the germination,
seedling and vegetative phases.

Plant Measurements at End of Reproductive Period. These
are to be generally the same as those made at the ends of the
preceding periods, but it will be desirable to separate the grain
produced from the rest of the tops in the present case. The dry
weight of grain is to be determined, also the number of grains.
Of course visual observations are to be made from time to time
during the reproductive phase, with special attention given to
flowering and fruiting.

Renewal of Solutions.

The solution placed in any culture jar as the beginning of an
experiment is to be completely discarded and replaced by a fresh
one of the same composition, after 31/2 days, and this renewal of
every solution is to occur at 31/2 -day intervals (twice per week,
thus avoiding Sunday renewals) throughout the course of the
experiment. The following points apply to all growth phases
alike.

Before the renewals are to be made, a new set of jars are pre-
pared, as at the beginning, each filled with its proper solution
and properly marked and stoppered with non-perforated cork.
Then these jars are placed near the series of cultures and each
stopper, bearing its plants, is removed from its original jar and
placed in the new jar of corresponding number. In making the
change, care is of course to be taken not to injure the roots nor
to disturb them more than is unavoidable. Finally, the opaque
jackets are transferred to the new jars, and the old jars are
emptied, the volume of the contents is recorded, and they are
washed, to be used again at the next renewal.

The purpose of determining the volume of solution remaining
in each jar at each renewal is to furnish data on the relative
amounts of water absorbed by the various cultures. The volume
of solution originally placed in each jar will of course be known,
and this value minus the volume left after 31/2 days will repre-
sent the volume absorbed in that period. The rate of absorption
is approximately the same as the rate of transpiration for such
plants as we deal with. Of course this volume measurement
need not be of great precision ; a plus or minus error of as much
as 3 or 4 per cent, is probably allowable until results indicate
necessity for greater precision. It should be added that a better
method of dealing with this feature is to weigh each culture be-

» 19

fore and after each filling of the jar with fresh solution. It is de-
sirable to employ the weighing method for such work as this, but
experience suggests that many experimenters prefer the volu-
metric method. Either will serve our purpose, however. In
either case the desideratum is to have a record of the approxi-
mate amount of solution removed from each jar during each
three and one-half day period.

Experiment Location and Exposure.

The cultures are to be exposed generally in a greenhouse, but
at some stations they may be out of doors. In any event, they
are to receive the climatic light (with shade, as of painted glass,
etc., only when this seems necessary in order that the plants may
thrive), but they must not receive any rain. For the colder
months at most stations the temperature will be artificially
much above the climatic temperature. When artificial heat is
not considered as necessary it will of course be omitted ; in gen-
eral, any greenhouse in which other plants are kept growing
should be suitable for these cultures. It is planned to carry out
these tests with a large number of climatic complexes, such as
will be obtained by employing a large number of geographical
locations and various seasons of the year at each station.

The special problem of uniform exposure to the aerial complex
of conditions (uniform for all cultures of any comparable series)
is of considerable importance, and it is hoped that all experi-
menters will use rotating tables. This point has been discussed
by Shive (1915) , who describes one way to build a rotating table
for this sort of work. It is desirable that all cultures that are to
be comparable should stand on the table in a single circle; two
circles of them form two series with slightly different aerial
surroundings, although the different cultures of any one circle
are themselves comparable. (If a rotating table cannot be em-
ployed, the cultures should be shifted on the bench so as to pass
through each position of exposure every few days; it. is well to
shift them daily according to a definite plan.)

Rotating tables built on motor-cycle wheels can be supplied by
the Plant World, but it is probably best for each cooperator to
superintend the building of his own. Tripod bases can be sup-
plied at $15.00 apiece, just the casting. Five-ply wood circles,
painted, four feet in diameter, can be supplied at $12.00 apiece,
packing included. The bearing portion may be built of a bicycle
hub, etc., in various ways that will suggest themselves, and
second-hand wheels may perhaps be obtained in some places.

20 ,

A satisfactory rotating bearing (with an insufficient reducing
gear) is offered by Winfield H, Smith, Buffalo, N. Y., and the
table top may be attached to this, which itself may be attached
to a greenhouse bench or other suitable support. The same firm
offers an excellent reducing gear (which is needed besides the
one coming with the bearing, and which is of course needed with
any table built on a bicycle wheel) . A finer type of gear was
recently supplied by the Eberbach Company, Ann Arbor, Mich.
The electric motor for this work should be of a rating of about
14 horse-power. It is to be remembered that the motor and
table operate continuously, night and day, for many weeks or
even months at a time, and proper lubrication is of course
essential.

Records of Aerial Conditions.

The non-solution conditions will not be controlled in these
tests; the complex of these will vary from hour to hour and
from day to day for any series, and it will differ from season to
season at the same station and from station to station at the
same season. In order to secure a rough description of this com-
plex for each experiment, four kinds of records are to be ob-
tained. These have to do with (1) air temperature, (2) reading
of white spherical porous-cup atmometer, (3) reading of black
spherical porous-cup atmometer, and (4) duration of sunshine.
Methods for these records are set forth below.

(1) The records are to show the maximum and minimum
air temperature in shade at the experiment location for every day
of each experiment. These records may be obtained by the use
of a max.-min. thermometer (read daily after the occurrence of
the maximum for the day) , or they may be taken off from a ther-
mograph record sheet. The data are to appear in terms of the
centigrade scale.

(2), (3) Standardized black and white spherical atmometer
cups, with simple mountings, will be furnished by the committee
at cost ($10.00 for two whites and two blacks, with two simple
mountings) . Orders should be sent to Baltimore. The two in-
struments should stand on the rotating table, within the circular
area left free by the peripheral row, or rows, of cultures. They
should be operated with distilled water, the porous surfaces
should be scrubbed with distilled water and a tboth-brush once
a week, and they should be read weekly, always at the same hour
of the day. Since water is apt to enter the instrument during the
operation of scrubbing, this operation should take place after

21

the reading and before the final setting of the instrument for the
next week's run. The best way to obtain readings is to weigh
the entire instrument at the beginning and end of each weekly-
run. The weekly procedure is consequently as follows: weigh
the instrument, scrub the sphere, wipe off what water clings to
tube, stoppers and bottle, add water to bottle more than suffi-
cient for the next run, and reweigh. The loss in weight by evapo-
ration for each week constitutes the weekly reading, and five of
these data for each type of instrument are needed for the five-
week period of the seedling phase. These data will give evidence-
of the kind of evaporation and sunshine conditions to which the
plants have been subjected.

At the end of a given series the spheres are to be dismounted
and dried, wrapped in paper, and sent (in a strong container and
by parcel post) to the Laboratory of Plant Physiology, Johns
Hopkins University, Homewood, Baltimore, Md. They will be re-
standardized, and the new coefficients will be sent to cooperators.
The spheres will be returned, or other ones will be sent in their
place (in case they seem injured) . (On operation of porous-cup
atmometers see: — Livingston, B. E., Atmometry and the porous-
cup atmometer. Plant World 18: 21-30, 51-74, 95-111, 143-149.
1915. Reprints may be procured from the Plant World, Tucson,
Ariz. The second pair of spheres is to be used during the time
required for restandardization.

(4) Sunshine records are to be obtained for the period of each
experiment series, from the nearest U. S. Weather Bureau Sta-
tion operating a Marvin sunshine-recorder, these records being
in the form of the daily duration (hours) of sunshine, as shown
by that instrument.

THE CULTURE SOLUTIONS FOR ALL PHASES.

Introduction.

It is obvious that there are actually an infinite number of
different solutions that must needs be tested if we are to find out
just what solution is the very best for a given plant and for a
given growth phase. Of course our experimentation must merely
approach finding this best solution and it must proceed by sam-
pling the range of solution possibilities (or promising portions of
that range) , as it were. It is highly desirable that the sample
solutions be selected, for the beginning, at uniform intervals
throughout any promising range of possibilities, and that the
intervals be not so broad as to let the best solution in the region
(for which we are looking) escape being fairly represented by

22

one of the samples tested. On the other hand, the intervals be-
tween the solutions selected for test — out of the infinite number
of possible ones — might be made so narrow that the large num-
ber of tests required would render the whole project hopeless.
We cannot hope to test millions of different solutions, nor should
we hope for much real progress if we were to test only a dozen,
for instance. In arranging the scheme of solution to be first
tested, as presented below, the judgments of a number of spe-
cialists in this general field have been combined. It must be
remembered that the present plan does not pretend to lay out
the experimentation excepting for the beginning of our work.
We begin by sampling a certain region only of the whole infinite
field of solution possibilities. Other regions may be attacked
later.

We proceed on the general physiological principle that the
best solutions for plant growth must always contain at least
some of each of the seven chemical elements known to be essen-
tial for all plant activity : K, Ca, Mg, Fe, N, P. and S. It appears
safe to say that it would be useless to test any solution not con-
taining all of these elements, in a search for the best solution for
any plant and growth phase. Consequently, under the guidance
of our present knowledge, we do not need to deal with any solu-
tion that does not contain all of the seven recognized essential
elements for higher plants in general.

Furthermore, experience has already shown that no solution
may be expected to support good plant growth if it contains more
than a small trace of iron. On this account, and because agri-
culture seldom meets with either a deficiency or an excess of iron-
as a source of trouble, we shall at first make no study of different
partial concentrations of that element. We shall follow Tot-
tingham in supplying iron as FePO' in the same, very small,
amount to every solution employed after the germination phase.
(For that phase the suuply of iron in the seed may safely be con-
sidered as sufficient.)

It is of course logically possible (perhaps even probable) that
the very best solution for any plant and phase may eventually be
found to contain still other elements besides the seven recognized
essential ones. We shall ignore this proposition at the beginning
of our work, however, and shall study only solutions containing
just the six elements K, Ca, Mg, N, P, and S, in various propor-
tions and in various total concentrations, besides a trace of Fe.
Later plans will perhaps introduce some of the apparently most
promising non-essential elements, such as Na, CI, Si, Mn, etc.,

23

but it would be quite hopeless to attempt to bring these into con-
sideration at the start, especially considering the limited number
of cooperators available. It should be remarked that there will
surely be a considerable amount of silicon in all the solutions
tested (since uncoated glass containers are to be employed), but
the amount of this element present may be considered as prac-
tically the same in all solutions. Like iron, it will be uniformly
present in small amount. The same is true, to a degree, of
sodium ; and to a smaller degree of chlorine. But the traces of
these three elements that may be present are ignored for the
part of the project now being planned.

From these considerations it emerges that our present plans
involve simply the testing of solutions containing the six ele-
ments that are essential in considerable quantities, with addi-
tion of a trace of the seventh essential element, Fe. As Shive
(1915) has pointed out, the simplest way to get these six ele-
ments into solution is to prepare the solution from three salts;
since three of the elements occur as kations and the other three
occur in anions. It appears best, at the start, to employ N as
the nitrate ion (NOO, P as the di-hydrogen phosphate ion
(H^PO*), and S as the sulphate ion (SO*). Other carriers of
these three elements may be studied later, such as nitrates, am-
monium salts, mono-hydrogen phosphates, sulphites, etc. It is
even probable that ammonium may need to be introduced for
later growth phases of soy bean to get even presentable growth,
but this matter is not now before us.

Of course it may be that no possible three-salt solution is best
suited to the growth of a given plant in a given developmental
phase ; it is clear that there are many sets of element or ion pro-
portions that cannot be obtained in a three-salt solution at all,
and four-, five-, six-, etc., salt solutions must logically be brought
into the experimental comparison before the very best possible
six-ion solution may be established. It seems desirable, however,
to make a very thorough study of the three-salt possibilities be-
fore moving forward to attack the much more complex types of
solution with more than three salts. One type of such solution
has been studied by Tottingham (1914) for young wheat plants.
As our project goes forward, plans for later campaigns may be
formulated, but an attempt at their consideration would be boot-
less at present.

The Three-Salt Solutions Characterized.

As Livingston and Tottingham have pointed out (Amer. Jour.
Bot. 5: 337-346. 1918. A reprint may be obtained from either

24

author), there are exactly six possible types of three-salt solu-
tions that can be made to contain just these six ions, K, Ca, Mg,
H2P0% N0% and SO', and it is a rather thorough test of these six
types that is contemplated for the first stage of the present
project.

It should be added that there are three other essential ele-
ments, besides the ones mentioned above, that are always present
in any of these solutions; namely, C, H, and 0. The solution is
mostly water, oxygen occurs as a solute and also in every one of
the three anions employed, hydrogen occurs in the di-hydrogen
phosphate ion, and CO- occurs as a solute (thus adding the ele-
ment C). It may be that the oxygen atom in an ion will prove
to be negligible in such work as this (it seems not to have been given
serious consideration in any of the published discussions of
nutrient solutions and fertilizers), but it is certain that the
H-ion, as such, is of great importance in determining the physio-
logical properties of nutrient solutions for plants. (See, for
example: — Sorenson, S. P. L. Ueber die Messung und Bedeu-
tung der Wasserstoffionenkonzentration bei biologischen Prozes-
sen. Ergeb. Physiol. .12: 393-532. 1912. Sharp, L. T., and
D. R. Hoagland. Acidity and absorption in soils as measured by
the hydrogen electrode. Jour. Agric. Res. 7: 123-145. 1918.
Plummer, J. K. Studies on soil reaction as indicated by the
hydrogen electrode. Jour. Agric. Res. 12: 19-31. 1918.)

The six possible types of three-salt solution are represented
below, the arrangement being the same as that employed by
Livingston and Tottingham (1918). On the basis of present
knowledge the presence of carbon dioxide in these solutions may
be ignored as without significant influence upon the plants.

I. II. III. IV. V. VI.

Ca(N03)t Ca(N03)2 Ca(HaP04)3 CaCHsPOO* CaSO* CaSO*

KH=PO* K2SO1 KNOs K2SO4 KNO. KH^PO*

MgSO* Mg(H2PO*)2 MgS04 Mg(N08)» Mg(H2PO0* Mg(NO«)t

Our first problem is to find (by actual test with each growth
phase) the best set of volume-molecular proportions and the
best total concentration for each type of solution. Now, there
is clearly an infinite number of possible sets of proportions of
any three things, and for each set of salt proportions of each of
the six types there is an infinite number of total concentrations.
We choose, from the very large series of different sets of salt

25

proportions possible for each solution type, just twenty-one;
and we select them so as to be representative of the mathematic-
ally possible range of sets of proportions. This is accomplished
by letting the volume-molecular partial concentration of each
salt differ from solution to solution (in a series of twenty-one
solutions, all with the same total concentration, measured osmot-
ically) by increments of one-eighth of the total volume-molecu-
lar concentration. Previous workers in this field have mainly
used increments of one-tenth, and have employed osmotic pro-
portions instead of volume-molecular proportions. For each of
the six types of solution (numbered in Roman numerals above)
all the possible sets of salt proportions, with increments of one-
eighth, are represented by the points in a triangular diagram,
as first used in this sort of work by Schreiner and Skinner (U.
S. Bur. Soils, Bull. 70, 1910. Also Bot. Gaz. 50: 1-30. 1910.)
and later by Shive, McCall, Hibbard. (See Shive — 1915 — for
the general plan of such a diagram, but it is to be remembered
that he used increments of one-tenth and thirty-six sets of pro-
portions, while we employ increments of one-eighth and have
only twenty-one sets.) In diagraming the solutions for the
present project it is earnestly requested that all diagrams follow
the same system. Let the base line for the potassium salt be the
base of the triangle, and let that for the calcium salt be the left
side. The right side will then be the base line for the magnesium
salt, Each of these three base lines represents a row of solu-
tions each having one-eighth of its total volume-molecular con-
centration due to the salt for which the line is named. The apex
opposite this lipe represents a solution in which six-eighths are
due to that salt. The volume-molecular proportions of all three
salts are quickly determined for any solution represented on the
diagram. The diagram is given herewith. To designate the
solutions, the rows on the
diagram are numbered R6

from below upward, and
the solutions are numbered
in each row from left to
right. To refer to a solu-
tion we first write the
Roman numeral denoting
the type (what three salts
are used), then we write

the row number (preceded , , , , ,

by the letter R), then we SI S2 S3 S4 S5 S6
write the solution number

26

R5

R4

113

R2

• •
Rl

in the row, preceded by S) , and finally we state (in parentheses)
the total concentration, in terms of atmospheres of osmotic pres-
sure representing the calculated osmotic value of the solution in
question. Examples are:— IR2S3 (1.00 atm.), IIIR1S2 (1.50
atm.), VR6S1 (1.65 atm.), etc. This form of notation is em-
ployed in the tables given below, and it is hoped that all coopera-
tors will adhere strictly, in order to facilitate comparisons.
(Previous writers have employed C in placer of S, but it seems a
little better to use S as standing for solution rather than C, de-
noting culture.)

Blank triangular diagrams, printed on sheets SV^xll in., may
be obtained from Baltimore at a price of $1.00 per hundred.

Aside from the kinds of salt entering into one of these solu-
tions (solution type) there are four characteristics by which
that solution may be distinguished: (1) volume-molecular salt
proportions, (2) osmotic salt proportions (see Tottingham,
1914), (3) total volume-molecular concentration (proportional
to the number of molecules, of all kinds, per liter) , and (4) total
osmotic concentration (taken to be proportional to the number
of particles, — molecular groups, molecules and ions, of all kinds,
— per litre; this last characteristic may be expressed in various
ways, but the atmosphere will be the unit here used as a measure
of the calculated osmotic value, or the calculated potential
osmotic pressure (of which the solution is taken to be capable) .
On account of ionization (and probably hydration), nos. 1 and 2
do not vary proportionally to each other from solution to solu-
tion in our series ; nor do nos. 3 and 4. It follows that if we plan
our series of twenty-one solutions to vary by definite increments
on the basis of no. 1 (volume-molecular salt proportions), then
they must vary irregularly in respect to no. 2 (osmotic salt pro-
portions). The variation cannot be regular by both criteria at
once, and we have chosen the former as the one to be used. This
criterion (no. 1) can be definitely stated for any of the solutions
without any assumption regarding ionization, osmotic phe-
nomena, etc. On the other hand, since the total concentration
of a solution must act upon plants primarily in an osmotic way,
the calculated osmotic value (no. 3, above) is here used for this
measure of the main physical character of any solution. This
usage involves calculation, and assumptions as to ionization, or
direct measurements of the lowering of the freezing-point, but
it seems desirable (at the start, and in spite of uncertainties)
to compare all the twenty-one selected sets of salt proportions,
keeping the calculated total osmotic value constant throughout

27

each series. The dilutions shown in the tables given below are
based on freezing-point determinations made by Dr. Shive, espe-
cially for this work. Other plans of dilution (which cannot alter
the volume-molecular salt proportions in any given case) may of
course be employed. The osmotic values are to be considered as
much less precise than the salt proportions.

In this general connection, it may be noted that actual ionic
partial concentrations of the various salts in any of these three-
salt solutions is at present impossible to determine (with the
single exception of the hydrogen-ion, for which a method is of
course available) , and any mental picture of assumed values
of the degrees of ionization of the various kinds of salt molecules
must depend upon more or less probable assumptions, for the
actual testing of which no methods have yet been devised. The
physical chemistry of such three-salt solutions as these is still
far beyond us, excepting in its most general aspects. But physi-
ology and agriculture need not wait for the advance of physical
chemistry in this connection ; we aim to determine the physio-
logical properties of our solutions (by plant tests) and merely to
define our solutions in such a way that they may be reproduced
at any time in the future, for advanced physical-chemical study,
etc. Any solution is sufficiently defined for exact reproduction
when the volume-molecular partial concentration is stated for
each of the salts used.

For a beginning, we wish to compare the twenty-one different
sets of salt proportions for each of the six types of solution and
for the same total osmotic concentration throughout the entire
series. The uniform total concentration adopted should be one
that promises to be suitable for good growth of the plants, and,
at the same time, it must be such that all of the solutions may be
possible in this concentration without the formation of precipi-
tate. The osmotic value of 1.00 atmosphere at 25° C. is chosen
as the index of this uniform total concentration. There are thus
126 different solutions (really only 123, see below) to be com-
pared in the beginning, all having the same osmotic value (1.00
atm.), but all differing in other ways (salt proportions or kinds
of salts used).

The formulas for the 126 solutions, and fpr the universal con-
trol solution (Shive's IR5C2, increments of 1/10, 1.75 atm.) are
given in the accompanying tables, which have been prepared by
Dr. Shive for this project. It will be noted that there is a sepa-
rate table for each of the six types of solution and that each table
presents the twenty-one different sets of volume-molecular salt

28

proportions for its own type. In each table, the first column
shov/s the twenty-one solution numbers, the next three columns
present the volume-molecular proportions of the three salts used,
and the remaining three columns give the actual volume-molecular
partial concentrations of the three salts — the latter always stated
for a mixture having a total osmotic value of 1.00 atmosphere.
The reader should be warned that the relative partial concen-
trations cannot be read vertically ; for example, in table I it can-
not be said that the volume-molecular partial concentration of
KH-PO^ is the same in all solutions of row 1, etc., although the
relative proportional values for this salt are all set down as unity
for these solutions. The data of the last three columns of the
table show how this comes about ; the unit used in reckoning the
relative proportions steadily becomes smaller as we proceed
along the row from left to right (on the triangular diagram).
This reduction is necessary on account of the phenomena of ioni-
zation, etc. (as evidenced when the complete solutions are sub-
jected to the freezing-point determination), and on account of
the desideratum that all solutions should have approximately the
same osmotic value (1.00 atm.) . But the relative salt proportions
for each individual solution are stated correctly if simply read
from left to right in the table; thus, for IRISI, KH^PO*:
Ca ( NO 0 - : MgSO^ : : 1 : 1 : 6, etc. It will be noted that the proportions
of elements and ions may be read in a similar way, note being
taken of the number of atoms or ions in each molecule considered.
Thus, K:Ca:Mg :: 1 :1:6 ; but PO^: NO^: SO^:: 1:2:6, andH:N:
S: : 2:2:6. The proportions of the three kations K, Ca, and Mg
are read directly from the position of the solution on the triangu-
lar diagram for types I, III, V and VI, since none of the mole-
cules used for these types gives more than a single one of these
ions. For the other two types it must be remembered that there
are two K ions in each molecule of K-SO^. (In this last considera-
tion is will be noted that the term "ionic proportions" refers to
atoms or atomic groups — Ca, POs etc. — as ions, without regard
to the actual degree of dissociation of the corresponding mole-
cules. When we say that the ionic proportions of a solution
are: — PO*: SO^: NO'': : 1 :2:6, we merely signify that these
atomic groups were placed in the solution in these proportions,
not implying at all that the ionized portion alone shows such
proportions.)

29

TABLE I. SOLUTIONS OF TYPE L

Partial volume-molecular concentrations and molecular proportions of
KH2PO*, Ca(N03)2, and MgSO* in 21 solutions all having a calculated
osmotic value of approximately 1.00 atm. at 25 °C., but differing (by in-
crements of % ) in salt proportions.

The highest partial volume-molecular concentrations of the salts of this
table, that may be used in stock solutions (mixed) without change in the
molecular proportions, are obtained, in each case, by multiplying each value
given in the table by the factor 3.50. One liter of each of these strongest
stock solutions, properly diluted with distilled water, will make 3.50 liters
of nutrient solution with an osmotic value of approximately 1.00 atm. at
25°C.

Molecular Proportions.

Partial Volume-molecular Concentrations.

Solution
number.

KH3PO4

CaiNOs)!,

MgSO<

KHjPOi

Ca(N03)j

MgS04

IRISI

1

6

.0027

.0027

.0161

S2

2

5

.0025

.0049

.0123

S3

3

4

.0024

.0071

.0094

S4

4

3

.0022

.0089

.0067

S5

5

2

.0022

.0108

.0043

S6

6

1

.0020

.0122

.0020

R2S1

2

1

5

.0053

.0027

.0132

S2

2

2

4

.0049

.0049

.0099

S3

2

3

3

.0047

.0071

.0071

S4

2

4

2

.0045

.0090

.0045

S5

2

5

1

.0041

.0104

.0021

R3S1

3

1

4

.0076

.0025

.0101

S2

3

2

3

.0072

.0048

.0072

S3

3

3

2

.0068

.0068

.0045

S4

3

4

1

.0065

.0086

.0021

R4S1

4

1

3

.0099

.0025

.0074

S2

4

2

2

.0094

.0047

.0047

S3

4

3

1

.0090

.0068

.0022

R5S1

5

1

2

.0123

.0024

.0049

S2

5

2

1

.0118

.0047

.0023

R6S1

6

1

1

.0145

.0024

.0024

Control,

Shive's

R5C2 -(1.75 atm.)* 3.77 1.09 3.14

.0180

.0052

.0150

* Shive's solution was planned on the basis of osmotic proportions and
increments of 1/10 of the total osmotic value, so that the molecular pro-
portions when stated as eighths are not whole numbers. On the present
basis Shive's best solution is described as IR3.77 SI. 09 (1.75 atm.), and
its location is easily found on our triangular diagram.

30

TABLE 11. SOLUTIONS OF TYPE IL

Partial volume-molecular concentrations and molecular proportions of
KzSOi, Ca(NOs)», and Mg(HsPO«)a in 21 solutions all having a calculated
osmotic value of approximately 1.00 atm. at 25 °C., but differing (by in-
crements of % ) in salt proportions.

The highest partial volume-molecular concentrations of the salts of this
table, that may be used in stock solutions (mixed) without change in the
molecular proportions, are obtained, in each case, by multiplying each value
given in the table by the factor 3.70. One liter of each of these strongest
stock solutions, properly diluted with distilled water, will make 3.70 liters
of nutrient solution with an osmotic value of approximately 1.00 atm. at
25 °C. Instead of 3.70, the factor 3.00 is used, however (see Table VIII).

Molecular Proportions. Partial Volume-molecular Concentrations.

Solution
number.

Kj,SO« Ca(NO,),

Mgr(H,P04)2

K2SO4

Ca(N03)i,

Mg(HjPOJ,

RlSl

1

6

.0019

.0019

.0118

S2

2

5

.0019

.0039

.0097

S3

3

4

.0019

.0059

.0078

S4

4

3

.0019

.0075

.0056

S5

5

2

.0019

.0094

.0037

S6

6

1

.0019

.0116

.0019

R2S1

2

1

5

.0038

.0019

.0096

S2

2

2

4

.0036

.0036

.0072

S3

2

3

3

.0036

.0054

.0054

S4

2

4

2

.0036

.0072

.0036

S5

2

5

1

.0036

.0091

.0018

R3S1

3

1

4

.0057

.0019

.0076

S2

3

. 2

3

.0056

.0037

.0056

S3

3

3

2

.0056

.0057

.0038

S4

3

4

1

.0056

<•

.0075

.0019

R4S1

4

1

3

.0074

.0018

.0056

S2

4

2

2

.0074

.0037

.0037

S3

4

3

1

.0075

.0056

.0019

R5S1

5

1

2

.0094

.0019

.0037

S2

5

2

1

.0094

.0037

.0019

R6S1

6

1

1

.0112

.0019

.0019

Control, Shive's

R5C2 (1.75 atm.)

* 3.77

1.09

3.14

.0180

.0052

.0150

* See footnote to Table I.

81

TABLE III. SOLUTIONS OF TYPE III.

Partial volume-molecular concentrations and molecular proportions of
KNO», Ca(H2P04)2, and MgSOi in 21 solutions all having a calculated
osmotic value of approximately 1.00 atm. at 25 °C., but differing (by in-
crements of Vs ) in salt proportions.

The highest partial volume-molecular concentrations of the salts of this
table, that may be used in stock solutions (mixed) without change in the
molecular proportions, are obtained, in each case, by multiplying each value
given in the table by the factor 3.70 . One liter of each of these strongest
stock solutions, properly diluted with distilled water, will make 3.70 liters
of nutrient solution with an osmotic value of approximately 1.00 atm. at
25 °C. Instead of 3.70, the factor 3.50 is used, however (see Table IX).

Molecular Proportions. Partial Volume-molecular Concentrations.

Solution
number.

KNOi, Ca(H2P04)t

UgSOi

KNO,

Ca(Hi!POJi,

MgSO*

RlSl

1

6

.0027

.0027

.0165

S2

2

5

.0026

.0053

.0132

S3

3

4

.0024

.0073

.0098

S4

4

3

.0023

.0093

.0070

S5

5

2

.0021

.0106

.0042

S6

6

1

.0021

.0125

.0021

R2S1

2

1

5

.0054

.0027

.0135

S2

2

2

4

.0048

.0048

.0096

S3

2

3

3

.0045

.0067

.0067

/ S4

2

4

2

.0042

.0084

.0042

/ S5

2

5

1

.0041

.0103

.0020

^ R3S1

3

1

4

.0075

.0025

.0099

S2

3

2

3

.0070

.0047

.0070

S3

3

3

2

.0067

.0067

.0045

S4

3

4

1

.0064

.0086

.0021

R4S1

4

1

3

.0099

.0025

.0074

S2

4

2

2

.0093

.0047

.0047

S3

4

3

1

.0085

.0064

.0021

R5S1

5

1

2

.0125

. .0024

.0048

S2

5

2

1

.0113

.0045

.0023

R6S1

6

1

1

.0139

.0023

.0023

Control, Shive's

R5C2 (1.75 atm.)

* 3.77

1.09

3.14

.0180

.0052

.0150

* See footnote to Table I.

82

TABLE IV. SOLUTIONS OF TYPE IV.

Partial volume-molecular concentrations and molecular proportions of
K2SO4, C^(H2P04)2, and Mg(N03)2 in 21 solutions all having a calculated
osmotic value of approximately 1.00 atm. at 25 °C., but differing (by in-
crements of % ) in salt proportions.

The highest partial volume-molecular concentrations of the salts of this
table, that may be used in stock solutions (mixed) without change in the
molecular proportions, are obtained, in each case, by multiplying each value
given in the table by the factor 4.20. One liter of each of these strongest
stock solutions, properly diluted with distilled water, will make 4.20 liters
of nutrient solution with an osmotic value of approximately 1.00 atm. at
25 °C. Instead of 4.20, the factor 3.00 is used, however (see Table X).

Molecular Proportions.

Partial Volume-molecular Concentrations.

Solution
number. .

RlSl

S2
S3
S4
S5
S6

K2SO4 Ca(HjP04)j

1 1
1 2
1 3
1 4
1 5
1 6

Mgr(N03)i,
6
5
4
3
2
1

K2SO4
.0018
.0018
.0019
.0019
.0019
.0019

CaCHjPOi),

.0018
.0036
.0056
.0075
.0093
.0113

Mg(NO,)2

.0108
.0092
.0075
.0056
.0037
.0019

R2S1

S2
S3
S4
S5

2
2
2
2
2

1
2
3
4
5

5
4
3
2
1

.0037
0.037
.0037
.0038
.0038

.0018
.0037
.0056
.0077
.0097

.0091
.0074
.0056
.0038
.0019

R3S1
S2
S3

S4

3
3
3
3

1
2
3
4

4
3
2
1

.0056
.0056
.0056
.0057

.0019
.0037
.0056
.0075

.0075
.0056
.0038
.0019

R4S1
S2
S3

4
4
4

1
2
3

3
2

1

.0076
.0077
.0078

.0019
.0039
.0059

.0057
.0039
.0019

R5S1
S2

5
5

1
2

2
1

.0097
.0098

.0019
.0039

.0039
.0019

R6S1

6

1

1

.0116

.0019

.0019

Control, Shive's
R5C2 (1.75 atm.)

* 3.77

1.09

3.14

.0180

.0052

.0150

* See footnote to Table I.

33

TABLE V. SOLUTIONS OF TYPE V.

Partial volume-molecular concentrations and molecular proportions of
KNO3, CaSO«, and Mg(H2POi)2 in 21 solutions all having a calculated
osmotic value of approximately 1.00 atm. at 25 °C., but differing (by in-
crements of % ) in salt proportions.

The highest partial volume-molecular concentrations of the salts of this
table, that may be employed in the nutrient solutions of this series are
those actually given here.

Solution
number.

KNO«

RlSl

S2

S3

S4

S5

[S6*

R2S1

2

S2

2

S3

2

S4

2

S5

2

R3S1

3

S2

3

S3

3

S4

3

R4S1

. 4

S2

4

S3

4

R5S1

5

S2

5

R6S1

6

Control,

Shive's

R5C2(1.75atm.)

**3.77

Molecular Proportions.

Partial Volume-molecular Concentrations.

GaSO^ MgCHaPO^j

1.09

3.14

KN03

CaSOi

Mg(H2P04),

.0019

.0019

.0115

.0021

.0041

.0103

.0021

.0061

.0081

.0021

.0088

.0067

.0023

.0104

.0041

.0024

.0143

.0024]

.0041

.0021

.0104

.0042

.0042

.0083

.0044

.0067

.0067

.0043

.0085

.0043

.0048

.0121

.0025

.0065

.0023

.0086

.0066

.0044

.0066

.0072

.0072

.0048

.0074

.0098

.0025

.0086

.0022

.0065

.0091

.0046

.0046

.0094

.0071

.0024

.0112

.0023

.0045

.0113

.0045

.0023

.0139

.0180

.0024

.0052

.0024

.0150

* The solubility of CaS04, 2H2O is approximately .0140 m. Solution R1S6
is therefore not possible with an osmotic value of 1.00 atm.
** See footnote to Table I.

34

TABLE VI. SOLUTIONS OF TYPE VI.

Partial volume-molecular concentrations and molecular proportions of
KH2PO4, CaSO« and Mg(N0»)2 in 21 solutions all having a calculated
osmotic value of approximately 1.00 atm. at 25 °C., but differing (by in-
crements of Vs ) in salt proportions.

The highest partial volume-molecular concentrations of the salts of this
table, that may be employed in the nutrient solutions of this series are
those actually given here.

Molecular Proportions.

Partial Volume-molecular Concentrations.

Solution
number.

KH0PO4

CaSOi

Mk(N03)2

KH2P0*

CaSOi

Mg(N03)2

RlSl

1

6

.0020

.0020

.0116

S2

2

5

.0021

.0041

.0102

S3

1

3

4

.0022

.0065

.0086

S4

4

3

.0023

.0091

.0069

S5

5

2

.0024

.0120

.0048

[S6*

6

1

.0026

.0155

.0026]

R2S1

2

1

5

.0040

.0021

.0101

S2

2

2

4

.0044

.0044

.0087

S3

2

3

3

.0050

.0070

.0070

S4

2

4

2

.0053

.0107

.0053

[S5*

2

5

1

.0054

.0136

.0028]

R3S1

3

1

4

.0062

.0021

.0082

S2

3

2

3

.0068

.0045

.0068

S3

3

3

2

.0073

.0073

.0048

S4

3

4

1

.0079

.0104

.0027

R4S1

4

1

3

.0089

.0023

.0067

S2

4

2

2

.0093

.0047

.0047

S3

4

3

1

.0103

.0078

.0026

R5S1

5

1

2

.0120

.0024

.0048

S2

5

2

1

.0130

.0052

.0027

R6S1

6

1

1

.0146

.0025

.0025

Control,

Shive's

R5C2(1.

75atm.)**3.77

1.09

3.14

.0180

.0052

.0150

*The solubility of CaSO*, 2H2O is approximately .0140 m. Solutions R1S6
and R2S5 are therefore not possible with an osmotic value of 1.00 atm. «
** See footnote to Table I.

35

Preparation of the Solutions.

Introduction. The Baker Chemical Company, of Phillipsburg,
N. J., has very kindly agreed to prepare the salts needed for
this cooperation in special lots, and at cost, so that all of any
given salt will be of the same lot. These salts will be put up in
sealed bottles with a label to indicate this project of the National
Research Council, and the analysis (including the mean water
content) will be shown on the label. These salts may be obtained
from the above-named manufacturers by specifying that they are
needed for the Plant Nutrition Project of the National Research
Council. At the outset of our work salts from othefr lots will
have to be used, since it will take some time for the various
laboratories in this cooperation to obtain the special salts.
Orders should" be placed as soon as possible, and it will help the
work if the committee is informed by sending to Baltimore a
memorandum of the salts ordered when the order is sent to the
manufacturer. Cooperators are asked to do this.

The nutrient solutions are to be prepared by adding, in each
case, measured amounts of the single-salt stock solutions to a
measured amount of distilled water. The first operation is, con-
sequently, to make up the single-salt 'stock solutions.

The Single-Salt Stock Solutions. These should be made up so
as to have the following volume-molecular concentrations. They
will keep for a long time and should be tightly stoppered and
preserved in darkness.

KNO.,

. 1.00 vol.-mol.

CaSOi. 2H.0,

.. 0.013 vol.-mol

KH2PO4,

. 0.10 vol.-mol.

Mg(N03).. 6H2O, .

. . 1.00 vol.-mol

K2SO.,

. 1.00 vol.-mol.

Mg(H=P04)2,

. 0.10 vol.-mol

Ca(N03)2, 4H2O, .

. 1.00 vol.-mol.

MgSOi. 7H.0,

. . 1.00 vol.-mol

Ca(H2PO0^-,

. 0.40 vol.-mol.

The amount of salt to be used is weighed out and placed in dis-
tilled water in a volumetric flask or other suitable container,
being shaken from time to time until solution is complete after
which the solution is made up to required volume by adding water.
Heat may be applied to hasten solution in some cases, but it
would produce decomposition in others. It is best to dissolve all
salts at room temperature, excepting those noted below, for
which lower temperature is needed.

The three phosphates should be dissolved at temperatures
below 20° C, and calcium sulphate would be dissolved at a
temperature below 15° C. Its solubility limit is lower with

36

higher temperature and the concentration required (0.013 vol.-
raol.) is almost at the limit for ordinary temperatures. If the
larger crystals that are left when solution is nearly complete
are crushed with a glass rod the completion of the operation is
hastened.

It is well to have a chemical determination (analysis for one
element) made of each single-salt stock solution (or at least of
the first lot of solution made from a given bottle of salt) so as to
determine whether the concentration called for is actually
attained.

The Mixed Stock Solutions and the Nutrient Solutions Them-
selves. To prepare any mixed stock solution, find the three par-
tial molecular salt concentrations for that particular solution
(tables I-VI) and multiply each of these three values by the
factor given for this purpose. This factor is unity for solution
types V and VI ; it is 3.50 for types I and III, and 3.0 for types
II and IV. From the three values thus obtained (and from the
molecular concentration of each of the three corresponding
single-salt solutions) calculate the number of cubic centimeters
of each single-salt stock solution needed for making a liter of the
mixed stock solution in question (or several liters; for simplicity
these directions are made to read for a single liter). Add the
three numbers thus secured and subtract the sum from 1000,
to give the number of cubic centimeters of water required. Place
this amount of water in a suitable bottle and proceed to add the
proper amount of each ol the three single-salt solutions, begin-
ning with the least concentrated of these and ending with the
most concentrated, and shake thoroughly to insure mixing as
thiS liquid runs in from the burette. Of course other procedures
may be followed; this one is simple and requires no large volu-
metric flasks, but it does require the careful measuring of the
three single-salt solutions and of the water. Throughout all
making of solutions it will be well to estimate the range of error
introduced and to keep record of this for each step of the pro-
ceeding. (Thus, 1 cc. as actually used may be, perhaps, anything
between 0.98 and 1.02 cc, etc. This error will of course depend
upon the burettes used, the temperature variations, the care
exercised by the operator, etc.)

It will be noted that the mixed stock solutions are more con-
centrated than the corresponding nutrient solutions themselves
(as prepared to have osmotic values of 1.00 atm.), excepting for
types V and VI. In these two cases the mixed stock solutions are
the 1.00-atm. nutrient solutions themselves.

37

All stock solutions are to be preserved, tightly stoppered, in
darkness. The nutrient solutions to be actually employed in the
cultures are to be prepared, with proper dilution, from these
mixed stock solutions. The nutrient solutions may, of course,
have any calculated osmostic value below that of the mixed stock
solution. It is planned to begin the work using calculated osmotic
values of 1.0 atm. for all solutions and the data of tables I-VI all
refer to this value. The nutrient solutions themselves may be
preserved, tightly stoppered, in darkness (to prevent algal
growth, etc.), but it is undesirable to keep them too long, since
alterations might possibly occur. It seems safe to preserve
them as long as five or six weeks, but a more frequent prepara-
tion of new ones is probably desirable. There seems to be no
doubt that the stronger mixed stock solutions (types I-IV)
will keep indefinitely in darkness, as will also the single-salt
stock solutions. If solutions are preserved for very long periods
the solubility of the glass of the containers may become a consid-
erable feature. If the bottles are internally paraffined this pos-
sibility is largely removed.

Supplementary Tables. Tables VII-XII give the amounts of
water and of each of the requisite single-salt stock solutions that
are needed to make a liter of each of the most concentrated
nutrient solutions for each of the six different solution types.
For example, solution IRISI (table VII) is made by placing
924.7 cc. of water in a suitable container and then adding to it,
with shaking, first 9.45 cc. of molecular KH^POs then 9.45 cc.
of molecular Ca(N03)^ and finally 56.4 cc. of molecular MgSO^
Of course every single-salt stock solution is always employed
with the concentration shown in parentheses below the formula
for that salt in these tables. (See page 36 of this Plan.) The
stock nutrient solutions of types V and VI have an osmotic value
of 1.0 atmosphere, while those of types I-IV are more concen-
trated. The solutions of types V and VI cannot be generally
made with higher concentrations than this value of 1.00 atm.
From tables VII-X and from page 36 it is clear that the stock
nutrient solutions of types I and III are planned to be made 3.5
times — and those of types II and IV 3.0 times — as concentrated
as will be needed for solutions having an osmotic value of 1.00
atmosphere. Of course other procedures may be followed in
making the nutrient solutions actually used, but this plan sup-
poses that the stock nutrient solutions will be prepared as here
set forth, using the factor 1.0 for types V and VI, 3.5 for types
I and III, and 3.0 for types II and IV. (See p. 37 of this Plan.)

Solutions VR1S6, VIR1S8, and VIR2S5 are not possible with
an osmotic value of 1.00 atm.; they cannot be tested except in
series having a lower total concentration than this.

38

TABLE VII.

Supplementary for Solutions of Type I.

Volumes (cubic centimeters) of distilled water and of the single-salt
stock solutions required to make one liter of each concentrated stock nu-
trient solution of type I. The stock nutrient solutions thus made are each
3.5 times as concentrated as the corresponding nutrient solution having an
osmotic value of 1.00 atmosphere.

Solution
number.

H.O

KH2PO4

(l.Om.)

Ca(N03)ii
(l.Om.)

MgSOt

(l.Om.)

IRISI

924.7

9.45

9.45

56.4

S2

931.1

8.75

17.15

43.0

S3

935.85

8.4

24.85

32.9

S4

937.7

7.7

31.15

23.45

S5

939.45

7.7

37.8

15.05

S6

943.3

7.0

42.7

7.0

R2S1

925.8

18.55

9.45

46.2

S2

931.05

17.15

17.15

34.65

S3

933.85

16.45

24.85

24.85

S4

937.0

15.75

31.50

15.75

S5

941.9

i 14.35

36.4

7.35

R3S1

929.3

26.6

8.75

35.35

S2

932.8

25.2

16.80

25.20

S3

936.55

23.8

23.80

15.75

S4

939.80

22,75

30.10

7.35

R4S1

930.7

34.65 .

8.75

25.9

S2

934.2

32.9

16.45

16.45

S3

937.0

31.50

23.80

7.7

R5S1

931.4

43.05

8.4

17.15

S2

934.2

41.3

16.45

8.05

R6S1 932.45 50.75 8.4 8.4

Control,

R3.77S1.09

(1.75 atm.) 961.8 18.0 5.2 15.0

39

TYPE VIII.

Supplementary for Solutions of Type 11.

Volumes (cubic centimeters) of distilled water and of the single-salt
stock solutions required to make one liter of each concentrated stock nu-
trient solution of type II. The stock nutrient solutions thus made are 3.0
times as concentrated as the corresponding nutrient solution having an
osmotic value of 1.00 atmosphere.

Solution
number.

HaO

KsSOi

(0.4m.)

Ca(N03)2
(1.0m.)

Mg(Hi,POJ,

(0.1m.)

IIRISI

626.05

14.25

5.7

354.0

S2

683.05

14.25

11.7

. 291.0

S3

734.05

14.25

17.7

234.0

S4

795.25

14.25

22.5

168.0

S5

846.55

14.25

28.2

111.0

S6

893.95

14.25

34.8

57.0

R2S1

677.8

28.5

5.7

288.0

S2

746.2

27.0

10.8

216.0

S3

794.8

27.0

16.2

162.0

S4

843.4

27.0

21.6

108.0

S5

891.7

27.0

27.3

54.0

R3S1

723.55

42.75

5.7

228.0

S2

778.9

42.0

11.1

168.0

S3

826.9

42.0

17.1

114.0

S4

878.5

42.0

22.5

57.0

R4S1

771.1

55.5

5.4

168.0

S2

822.4

55.5

11.1

111.0

S3

869.95

56.25

16.8

57.0

R5S1

812.8

70.5

5.7

111.0

S2

862.2

70.5 '

11.1

57.0

R6S1 853.3 84.0 5.7 57.0

Control,

R3.77S1.09

(1.75 atm.) 961.8 18.0 5.2 15.0

40

TABLE IX.

Supplementary for Solutions of Type III.

Volumes (cubic centimeters) of distilled water and of the single-salt
stock solutions required to make one liter of each concentrated stock nu-
trient solution of type III. The stock nutrient solutions thus made are each
3.5 times as concentrated as the corresponding nutrient solution having an
osmotic value of 1.00 atmosphere.

Solution
number.

H,0

KNOj
(l.Om.)

CaCHsPOJ,
(0.1m.)

MgrS04
(l.Om.)

IIIRISI

838.3

9.45

94.5

57.75

S2

759.2

9.1

185.5

46.2

S3

701.8

8.4

255.5

34.3

S4

642.9

8.05

325.5

24.50

S5

606.8

7.35

371.1

14.70

S6

547.8

7.35

437.5

7.35

R2S1

839.3

18.90

94.5

47.25

S2

781.6

16.80

168.0

33.60

S3

726.3

15.75

234.5

23.45

S4

675.6

14.70

294.0

14.70

S5

618.

14.35

360.6

7.00

R3S1

851.5

26.25

87.5

34.7

S2

786.5

24.50

164.5

24.5

S3

726.3

23.45

234.5

15.75

S4

669.2

22.40

301.0

7.35

R4S1

851.9

34.7

87.5

25.9

S2

786.5

32.55

164.5

16.45

S3

738.9 ^

29.75

224.0

7.35

R5S1

855.4

43.75

84.0

16.80

S2

794.9

39.55

157.5

8.05

R6S1

862.8

48.65

80.5

8.05

Control,

, •

R3.77S1.09

(1.75 atm.)

961.8

18.0

5.2

15.0

41

TABLE X.

Supplementary for Solutions of Type IV.

Volumes (cubic centimeters) of distilled water and of the single-salt
stock solutions required to make one liter of each concentrated stock nu-
trient solution of type IV. The stock nutrient solutions thus made are each
3.0 times as concentrated as the corresponding nutrient solution having an
osmotic value of 1.00 atmosphere.

Solution
number.

H2O

KoSOi
(0.4m.)

Ca(H2P04)2
(0.1m.)

Mg(N03)a
(1.0m.)

IVRISI

900.1

13.5

54.0

32.4

S2

850.9

13.5

108.0

27.6

S3

795.25

14.25

168.0

22.5

S4

743.95

14.25

225.0

16.8

S5

695.75

14.25

279.0

11.1

S6

642.05

14.25

339.0

5.7

R2S1

892.45

26.25

54.0

27.3

S2

840.55

26.25

111.0

22.2

S3

788.95

26.25

168.0

16.8

S4

729.1

28.5

231.0

11.4

S5

674.8

28.5

291.0

. 5.7

1

R3S1

878.5

42.0

57.0

22.5

S2

830.2

42.0

111.0

16.8

S3

778.6

42.0

168.0

11.4

S4

726.6

42.7

225.0

5.7

R4S1

868.9

57.0

57.0

17.1

. S2

813.5

57.8

117.0

11.7

S3

758.8

58.5

177.0

5.7

R5S1

858.6

72.7

57.0

11.7

S2

803.8

73.5

117.0

5.7

R6S1

849.6

87.0

57.0

5.7

Control,

»»

''\

R3.77S1.09

(1.75 atm.)

961.8

is.o

5.2

15.0

i2

TABLE XI.
' Supplementary for Solutions of Type V.

Volumes (cubic centimeters) of distilled water and of the single-salt
stock solutions required to make one liter of each nutrient solution of
type V, with an osmotic value of 1.00 atmosphere.

KNO3 CaSOi Mg(H2P04)2

(1.0m.) (O.aiSm.) (0.1m.)

1.9 146.2 115.0

2.1 315.4 103.0

2.1 469.2 81.0

2.1 676.9 67.0

2.3 800.0 41.0

2.4 1100.0 ' 24.0]

4.1 161.5 104.0
/ 4.2 33.0.0 83.0

4.3 515.4 67.0

4.4 653.8 43.0
4.8 930.8 25.0

6.5 176.9 86.0

6.6 338.4 66.0

7.2 553.8 48.0
7.4 753.8 25.0

8.6 169.2 65.0

9.1 353.8 46.0

9.4 546.1 24.0

11.2 176.9 45.0

11.3 346.1 23.0

13.9 184.6 24.0

18.0 5.2 15.0

* Solution VR1S6 cannot be made with a total concentration value of
1.0 atm.

Solution

number.

H2O

VRISI

736.9

S2

579.6

S3

447.7

S4

254.0

S5

156.7

[S6*

R2S1

73*0.4

• S2

582.8

S3

413.3

S4

298.8

S5

39.4

R3S1

730.6

S2

589.0

S3

391.0

S4

214.3

R4S1

757.2

S2

591.1

S3

420.5

R5S1

766.9

S2

619.6

R6S1

777.5

Control,

R3.77S1.09

(1.75 atm.)

961.8

43

TABLE XIL

Supplementary foi- Solutions of Type VI.

Volumes (cubic centimeters) of distilled water and of the single-salt
stock solutions required to make one liter of each nutrient solution of
type VI, with an osmotic value of 1.00 atmosphere.

Solution
number.

HjO

KHzPOi
(1.0m.)

CaSOi
(0.013m.)

Mk(N08)
(1.0m.)

VIRISI

832.6

2.0

153.8

11.6

S2

672.3

2.1

315.4

10.2

S3

489.2

2.2

500.0

8.6

S4

290.8

2.3

700.0

6.9

S5

69.7

2.4

923.1

4.8

[S6*

2.6

1192.3

2.6]

R2S1

824.4

4.0

161.5

10.1

S2

648.5

4.4

338.4

8.7 •

S3

450.0

4.6

538.4

7.0

S4

166.3

5.3

823.1

5.3

[S5*

5.4

1046.1

2.8]

R3S1

824.1

6.2

161.5

8.2

S2

640.3

6.8

346.1

6.8

S3

426.5

7.3

561.4

4.8

S4

189.4

7.9

800.0

2.7

R4S1

807.5

8.9

176.9

6.7

S2

624.5

9.3

361.5

4.7

S3

387.1

10.3

600.0

2.6

R5S1

798.6

12.0

184.6

4.8

S2

584:3

13.0

400.0

2.7

R6S1

790.6

14.6

192.3

2.5

Control,

R3.77S1.09

-'

(1.7.5 atm.)

961.8

18.0

5.2

15.0

* Solutions VIR1S6 and VIR2S5 cannot be made with a total concentra-
tion value of 1.0 atm.

44

Iron in the Nutrient Solutions. The source of iron is -to be
added (as ferric phosphate) to each nutrient solution after it has
been placed in the culture jar, in every case. The bottle contain-
ing this phosphate is first to be thoroughly shaken, so as to fur-
nish a uniform suspension, and then a sufficient amount of the
suspension is to be transferred to the culture jar (with a 1-cc.
pipette) , so as to add approximately thr-ee mg. of the precipitate
to each quart jar. After this addition the jars are ready for the
plants.

The preparation of the precipitated FePO* should proceed as
follows : In a bottle with capacity of 2 liters or more place 500
cc. of a 0.04 vol.-mol. solution of KH=PO^ and add thereto, with
agitation, a weak solution of ferric nitrate [Fe(N08)''], continu-
ing the addition until no more precipitate is produced. There
should thus be formed about 0.02 gram-molecule of FePOs which
should remain in suspension for considerable time, eventually
settling to the bottom of the bottle.

Now fill the bottle nearly full of distilled water, shake thor-
oughly and stand aside till nearly all the liquid is clear. Carefully
siphon off the clear liquid without loss of the precipitate, and
repeat the filling, shaking, settling and decanting process several
times, to wash the FePO^ free from KNO-' and any excess of
Fe(NO0' that was originally added. The washing should be
thorough, so that 1 cc. of the wash-water, evaporated at from
50° to 60° C, in a porcelain dish, shows no residue. Now trans-
fer all the precipitate, with its water, to a graduated liter-flask
and add distilled water to make a liter. Preserve in a tiglitly
stoppered bottle. When shaken thoroughly the suspension thus
formed should contain approximately 0.02 g.-mol. of FePO*,
about 3 g. per liter, or 3 mg. per cubic centimeter. It will be well
to prepare enough FePO* to last for a year or two of this work.

Enough of the uniform suspension is to be added to each quart
jar at each filling to give 3 mg. of FePO*. Of course it will not
dissolve appreciably, but it will furnish a constant and adequate
supply of iron. This material is not to be added to the germina-
tion solution, however, as has been said.

Repetitions of the Experiments. It is planned that all of the
sets of salt proportions (excepting the three that are impossible
with that concentration) will be tested at least once with an
osmostic value of 1.00 atm. The tests are to be carried out by
solution types, so that different cooperators may be working
with different types at the same time. The prehminary experi-
mentation for any cooperator may thus consist in the testing of

45

one set of 19, 20 or 21 cultures (and the triplicate control) , As
soon as a type group has been tested once, the best seven solu-
tions are to be selected, and all future work in this part of this
project is to be confined to these best seven sets of salt propor-
tions. This feature of the plan soon eliminates two-thirds of
the solutions, and it is based on the assumption that the best
seven solutions in any experiment will probably include the single
very best solution of that type in any other experiment, no mat-
ter when or where such other experiment may be carried out.
While climatic conditions may shift the position of the best physi-
ological balance of the entire group in the series of the best
seven sets of salt proportions, it is at least improbable that they
will shift this position to one outside of this series of seven. If
it should develop that none of the solutions of some type give
even fair growth— as compared to the control — then the whole
of that type may be eliminated. It is thus seen that the repeti-
tion will deal with at most no more than forty-two different sets
of salt proportions. These repetitions are to be carried out re-
peatedly and under a great variety of climatic complexes, and it
is really with these forty-two (or fewer) sets of salt proportions
that the present phase of our campaign is to deal. .

When the repetitions are taken up, other total concentrations
are to be introduced, besides the one having an osmotic value of
1.00 atm. Detailed plans in this connection may be postponed
till later, however. Plans for dealing with various logically
possible complications in other aspects of the research may also
be deferred till such complications actually arise from experi-
mental results.

SAND-CULTURES OF WHEAT.

Introduction. The sand-culture method to be used is essen-
tially that described by McCall (1916). The important feature
is that the nutrient solution is renewed at frequent intervals, in
much the same way as with water-cultures. As in all experi-
mentation of this cooperation, it is necessary that essential de-
tails be alike in all experiments if the results are to be com-
parable. The nutrient solutions to be used are the same as those
for water-cultures, so that there are one hundred and twenty-six
different sets of salt proportions in sand-cultures to be compared,
besides the general control, with Shive's solution IR5C2 (1/10-
increments, 1.75 atm.). This last is our solution IR3.77S1.09
(see table I). The following plan is based on a memorandum
furnished the committee by Dr. McCall and Dr. Shive.

46

Sand. The sand to be employed should be as nearly like that
used by McCall as is possible. (A sample may be obtained from
Dr. A. G. McCall, Maryland Agric. Exp. Sta., College Park, Md.)
This sand shows about 98 per cent, of SiO^ The grains are not
much rounded (artificially crushed quartz should not be used
in the present cooperation nor should thoroughly rounded sand
be used) . The mechanical analysis (by sieves) shows the follow-
ing proportions as to diameters of particles: 1.0 to 0.5 mm.,
1.4 per cent.; 0.5 to 0.25 mm., 86.4 per cent.; 0.25 to 0.10 mm.,
11.5 per cent.; 0.10 to 0.05 mm., 0.7 per cent. It has a water-
holding capacity of 31 per cent., on the dry-weight basis (Hilgard
method, with a column one cm. high. (See Hilgard, Soils, page
209). It should be remembered that the washing process re-
moves much of the most finely-divided material, so that the data
just given are applicable to the sand after washing. A sand that
does not satisfy these requirements may be corrected by addition
or removal of proper amounts of certain groups of particles
(using sieves). The water-holding capacity should agree with
that stated above, within a range of plus or minus one per cent. ;
that is, it may have any value between thirty and thirty-two per
cent, (dry-weight basis).

Before using, the sand is to be thoroughly washed, with tap or'
well water and then with distilled water. Washing is to be accom-
plished as follows: Fill a large glazed crock (about five-gallon
capacity) about two thirds full of water and pour sand into this,
stirring vigorously until crock is about two-thirds full of sand.
Then direct a stream of water into the sand (as by inserting end
of garden-hose nearly to bottom of crock), allowing water to
overflow at top of crock; continue this washing (with violent
agitation of the sand) until the overflow is free from sediment.
Decant, refill crock with distilled water, stir sand vigorously, and
decant again. Refill with distilled water, stir and decant once
more. After second decanting of distilled water, spread sand
on clean paper and allow it to become air-dry, avoiding dust or
other foreign matter.

Prepai^ation of Crocks. For culture pots, cylindrical half-
gallon stoneware crocks (glazed within and without, but not
dark-colored externally) about 14 cm. high and 14 cm. in diam-
eter, are to be used. For definite reference, they should be
serially numbered with paint, and solution designations may be
marked on them with wax pencil.

Twenty-five hundred grams of air-dry washed sand is to be
used for each crock, which should fill it to within about two centi-

47

meters from the top. A glass suction tube (with inside diameter
about 4 mm., is to be placed vertically against the wall of the
crock, its lower end resting on bottom of crock and its upper end
extending about 1 cm. above the rim. This tube is to be placed
before sand is poured into crock and will be held in position by
the sand. The lower end of the tube is to be loosely plugged with
glass-wool and tufts of the wool are to extend one or two centi-
meters beyond the tube, so that sand may rest on these and thus
hold the plug in place.

A supply orifice is furnished by a paraffined paper cone (or a
100-cc. wide-mouth bottle with the bottom removed) , standing
at the center of the sand surface and embedded in it to a depth
of about two centimeters. The paper cone should be about six
centimeters high, four centimeters in diameter at its larger
(lower) end and two centimeters in diameter at its smaller
(upper) end. These cones are rolled from heavy paper, fastened
by a pin or paper-clip, and are heavily paraffined.

Record the total weight of crock, tube, cone and sand. Cone
is not permanently placed till after seedlings are in position.

The Seedlings. The seeds are to be soaked in germination
solution and allowed to germinate on the germination net, just
* as for water-cultures, the shoots being four centimeters high
when transplanting occurs. Selection is made just as for water-
cultures. It is of course desirable that all seedlings be as nearly
alike as possible.

Introduction of Seedlings. When seedlings are ready, some
nutrient solution is poured on to the sand, to moisten it (a liter
of solution should be ready, but only a little is used at the start) ,
the surface is levelled and the selected seedlings are introduced,
five in each crock. These are to be selected beforehand, as in the
case of water-cultures. They are planted so that the grains will
lie about one-half centimeter below the sand surface, equally
spaced, in a circle half-way between the supply cone and the wall
of the crock. A flat wooden dibble (like a spatula) about fifteen
millimeters wide and having a sharp edge is convenient for set-
ting the seedlings. (An ordinary pot label with broad end
thinned serves will.) Care should be exercised not to injure the
roots.

The supply cone is introduced in the center of the sand sur-
face after the seedlings are in place, its larger end downward
and embedded in the sand to a depth of about two centimeters.
Then nutrient solution is poured in through the cone until the
liquid surface is about one centimeter above the sand, and the

48

crock is slightly jarred to settle the sand about the roots of the
plants and to give a flat surface for the wax seal.

An aspirator is now connected to the suction tube and the
excess of solution is drawn off until the moisture content of the
sand is reduced to about sixteen per cent, (dry-weight basis).
The sand is then flooded a second time with nutrient solution, and
the excess is again removed, as just described. The aspirator
tube should be joined to the culture tube with a suitable bottle
intervening as a trap to catch the solution that is removed. This
bottle is to be marked so as to indicate when the desired volume
of solution has been removed, a device that will save many
weighings if the volume of solution added is known. The weight
of the seedlings may be neglected and the required moisture
content of the sand may have any value between fifteen and sev-
enteen per cent, (dry- weight basis).

The Wax Seal. To hinder evaporation from the soil, the free
sand surface is sealed with a mixture of eighty parts (by weight)
of "Parawax" and twenty parts of "Vaseline, White" (Ches-
brough brand). Have the mixture only warm enough to flow
freely, otherwise the plants may be injured where their stems
are in contact with the seal. Pour the wax over the sand sur-
face, so as to form a layer from two to four millimeters thick,
being sure that the wax forms a tight joint at its junction with
the crock wall and with the supply cone, also that it makes good
contact with the seedling shoots. (On wax seals, see : Briggs and
Shantz, Bot. Gaz. 51: 210-219. 1911.)

Manipulations During the Culture Period. At the end of each
314-day period each culture is weighed, and suflficient distilled
water is added (through the cone) to bring the sand moisture
content back to the original sixteen per cent,, and record is
kept of the amount of water needed. Then the excess liquid is
removed (aspirator) until the moisture content is about ten per
cent. Then the sand is again flooded with fresh solution and the
excess is once more removed, this time leaving the moisture con-
tent at sixteen per cent. The culture is then ready for the suc-
ceeding 31/^-day period.

From the records showing the amounts of distilled water
added to any culture are to be obtained data of transpirational
water loss. It will be seen that the amount of salt absorbed by
the plants is neglected (as though the plants absorbed only water
from the solution), but the error thus introduced will be more
truly negligible than the one that would be encountered if
nutrient solution were used in place of distilled water.

49

Growth Phases. These are the same as for water-cultures
with wheat. For the reproductive phase the plants will require
mechanical support. (See McCall, Jour. Amer. Soc. Agron. 10:
127-134. 1918.)

Location, Exposure, Climatic Records, etc. These are all the
same as for water-cultures with wheat.

The Plant Records. These are the same as for water-cultures,
excepting that the root weights require special manipulation.
The wax seal is removed and the contents of the crock are placed
on a wire sieve (about ten meshes to the inch) , through which
the free sand is washed with a stream of water. Then the roots
are severed from the tops, as in the case of water-cultures, and
the tops are treated as before described. The root systems of
all plants from the same crock (including the adhering sand)
are then brought together, dried at 102° C, and the dry weight
for each culture is determined. Then each mass of roots is
ignited in a weighed porcelain crucible till all organic matter has
been removed, the weight of the remaining mineral matter is
determined, and this value is subtracted from the original dry
weight of roots and sand, to give approximately the dry weight
of the roots alone. The errors introduced by this method are
negligible in this sort of work. (See McCall, Soil Science 2:
223. 1916.)

CULTURES WITH SOY BEAN.

Experimenters who wish to work with soy bean are requested
to communicate immediately with the committee. While the
general procedure for this plant will be similar to that for wheat,
yet some details must necessarily be different, and many of these
are not yet worked out by preliminary experimentation.

THE SUB-DIVISION OF THE PROJECT.

Introduction. — The following notes may serve as suggestions,
to aid cooperators in choosing their problems in the project. It
is hoped that cooperators will choose for their work those por-
tio^is of the plan in which they feel most interested. At the same
time, the committee will be glad to aid in this connection, and it
may be necessary (in order that all parts of the plan may receive
attention) for the committee to make special requests at a some-
what later time.

In the first place, it is strongly urged that every experiment
include at least three cultures with Shive's best solution for the

50

early growth of wheat, the solution called control in the preced-
ing pages. It is largely through these controls that climatic
conditions and different groups of solutions tested at different
times and places are to be compared. At a later time it may be-
come expedient to adopt some other solution as general control,
but the one mentioned is the logical one to use in the early stages
of our studies.

The following paragraphs aim to present some of the most
promising ways of grouping the one hundred and twenty-three
solutions that are first to be tested (osmotic value, 1.00 atm.).

Suhdivision by Types. Each set of 21 (or 19 or 20) solu-
tions (tables I-VI) furnishes a logical group for experimen-
tation. Such a group includes (with the triplicate control) 22,
23 or 24 cultures, which is a convenient number for an experi-
menter who does not devote nearly all his time to the work. It
may be noted that types V and VI involve some physical-chemical
difficulties not encountered with the others, and those who have
had experience with this sort of difficulty are urged to undertake
the study of these two exceptional types. Type I is the one on
which most of the earlier work has been done.

Of course it will be desirable, where possible, to carry out
each experiment with these type groups in duplicate, triplicate,
etc., and an experimenter may thus give his entire time to the
solutions of a single group.

It will also be desirable, especially where two or more experi-
menters can work together, that the full sets of several solution
types (or even all six of them) be tested simultaneously, in which
case a single triplicate control will serve for all sets.

Suhdivision Into Groups Smaller Than Type Groups. For
smaller groups than are represented by the six different types of
solution, any solutions may be selected, either merely at random,
or because of a personal interest. It will be especially desirable
to study and compare in this way just those solutions that have
already given good promise. For the seedling phase of growth
Shive's (1915) results and those of Livingston and Tottingham
(1918) are of special interest as indicating promising solutions.
A study of Shive's graphic summary (page 390) for his optimal
concentration will suggest small groups of solutions of type I
that may be profitably compared. Table 2 of Livingston and
Tottingham may furnish similar suggestions for type III. Many
other sources of similar suggestions will doubtless become avail-
able as soon as a few experiments has been carried out, and such

51

suggestions may already exist in unpublished' or published
records.

It is not necessary that the plan of subdividing by solution
types should necessarily involve the testing of all the solutions
of a given type at once. The solutions may be graphed on the
triangular diagram and then the diagram may be arbitrarily
divided into two or more regions, each region being considered
separately. Thus, the first ten or eleven solutions of any one
of the tables as here given may be considered as a first group,
the remaining solutions of that type constituting a second group,
to be tested after the first.

An experimental comparison of the physiological properties
of any single solution given in tables I to VI, with the control
solution, will constitute a valuable step toward the working out
of the plan. It is hoped that many workers who are not able to
devote a great deal of time to this project will nevertheless join
in the work, even by testing a single solution. Indeed, the study
of the relation of climatic conditions to growth may be greatly
advanced if a large number of experimenters will carry out cul-
tures with the control solution alone. If one could do no more,
it would be well worth while to get the plant measurements for a
number of control cultures, at any time during the year, of course
obtaining at the same time the climatic data mentioned in the
plan. The growth of wheat in Shive's best solution for this plant
might thus become a sort of common criterion by which different
climatic complexes (for different seasons and for different sta-
tions) might be compared, in terms of their influence on the
physiological processes of wheat.

As the work goes forward the committee will furnish further
suggestions as to the subdivision of the plan, upon request.

REPORTS OF RESULTS.

As has been said, all cooperators are strongly urged to send
to the committee all results obtained just as promptly as possible.
Forms for such reports will be supplied to cooperators on
request.

SUSCEPTIBILITY TO ATTACK BY BACTERIA OR FUNGI.

Emphasis has been recently placed on the observed fact that
a poorly balanced fertilizer treatment may not only produce
smaller or less well-developed plants than does a more nearly
perfect treatment, but such poor treatment may frequently also

52

produce plants of apparently satisfactory appearance, which
nevertheless are very unsatisfactory on account of a high degree
of susceptibility to injurious attacks by parasitic organisms.
Plant pathologists agree that the problem thus suggested is of
very great fundamental importance and that definite' information
in this general connection should be made available as rapidly
as possible. It is seen that this problem involves both pathology
and physiology. Susceptibility to the attacks of a certain para-
sitic fungus or bacterial form may be considered as one of the
physiological characters that need to be understood for agricul-
tural plants, and it is especially important that the relations be-
tween such susceptibility and the salt treatment of the plants in
question should receive attention.

It is consequently planned that cooperators in the present
project who are familiar with the experimental methods of plant
pathology may undertake experimentation in this field. Of
course such experimentation must needs deal with the plants
employed for the simply nutritional aspect of our problem; for
the beginning, with "Marquis" wheat and soy bean.

It is planned that suitable groups of solutions may be em-
ployed in either water-culture or sand-culture and that when
the plants have reached a proper stage of development they may
be all tested for different degrees of susceptibility by being simi-
larly inoculated with the fungus or bacterium. The final records
in this sort of study will of course deal with the relative amounts
of infection and with the relative degrees of injury produced by
infection.

In order that the results may be standardized, it is necessary
that the plants be grown according to the details of the foregoing
plan for work on salt nutrition itself, and it is practically neces-
sary that these inoculation experiments include uninoculated con-
trols having the same solution treatments as are given to the
inoculated cultures. The uninoculated cultures will then furnish
the regular plant measurement (of the foregoing plan), with
which similar data from the inoculated cultures are to be com-
pared. For an illustration, a duplicate water-culture series with
solutions of type I may be carried out until the end of the third
week of the seedling phase of wheat. At that time the visual
observations on the plants are to be made with special care, after
which one culture with each solution is to be inoculated and the
cultures are to be continued to the end of the five-week period of
this phase. Final observations and measurements are to be made
on all cultures. It is very essential that special attention be given

53

to the climatic conditions at the time of inoculation and later ; it
may be desirable to read the atmometers daily or even more fre-
quently, and to obtain thermograph tracings of the temperature
and special notes on the degree of cloudiness. The committee
will be glad to discuss forms of experiment in this field with any
cooperator who is interested. The details of such experiments
need to be worked out for each special case.

CHEMICAL COMPOSITION OF THE PLANTS AS RELATED

TO THE CHARACTERISTICS OF THE

CULTURE MEDIUM.

Besides the plant records mentioned in the preceding pages,
it is planned that the plants of selected cultures may be sub-
jected to chemical analysis, to determine the proportions of some
of their constituents, and that the results of these analyses may
be correlated with the characteristics of the media in which the
plants have been grown. Those who so desire may take part in
this aspect of the project by communicating with the com-
mittee, which will attempt to make arrangements by which one
cooperator may grow the plants while another performs the
analyses. These analyses are planned to deal with both mineral
and organic constituents of the plants.

^

54

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