50 
Journal of Agricultural Research 
Vol. XXIV, No. I 
absorbed was reduced by removing the plants from the nutrient solution 
for half the time. But when calculated upon the rate of absorption per 
day, both the plants in the strong solution and those in the weak had a 
higher rate when grown only half time in the nutrient solution. 
It is somewhat surprising to note that not only the rate of absorption 
but the general appearance of the plants—color, size, root development, 
and vigor of growth—is usually better when the plants are grown in a 
good nutrient solution for one period and in distilled water the next. 
This is not always the case but seems to be characteristic of plants that 
are grown during warm weather; when growth and absorption are rapid, 
and is not so likely to be true of plants grown in cold weather, when growth 
and absorption are relatively slow. Better looking plants are often ob¬ 
tained when they are kept in the nutrient solution at night and in dis¬ 
tilled water during the day. 
The experiments here described seem to demonstrate that a demand 
for plant food may exist within the plant, that this demand may be modi¬ 
fied in different ways, and that the demand may be determined by analyt¬ 
ical methods. The author has demonstrated the fact that it is possible 
to go out in the field, to take up a plant and put it in a full nutrient solu¬ 
tion, and to determine what plant food it is hungry for by the way it feeds 
upon the nutrient solution. 
TRANSFER OF PLANT FOODS WITHIN THE PLANT 
The plant seems to feed upon the ions and not upon the molecules, and 
no plant seems to require a base and an acid in exactly the proper pro¬ 
portion to form a salt. It has been shown by Breazeale and Briggs ^ that 
a plant is even particular as to the kind of ion that it absorbs. Plants 
that had a high demand for potassium when placed in a solution of ortho- 
clase were unable to feed upon the dissolved potassium. The solution 
was dilute, it is true, but not so dilute as to prevent the absorption of 
potassium. It is probable that the potassium existed in the solution as a 
double ion in combination with aluminum. The plant did not need and 
could not utilize the aluminum and therefore would not take up either the 
potassium or the aluminum. 
That the transpiration rate has little to do with absorption can easily 
be shown by placing a bell jar over a pan of cultures, cutting down the 
transpiration, and measuring the rate of absorption in comparison with 
controls. Plants will feed just as rapidly when transpiration has thus 
been reduced to a minimum as they will when transpiring a maximum 
amount of water. 
One can scarcely conceive of a plant feeding upon ions or exercising 
selective absorption in such a decided way if the transpiration stream or 
the osmotic concentration, or any other phenomenon except the specific 
demand of the plant, dominates the process of absorption. 
In the same way, practical field results indicate that all plants do 
not possess the same ability to feed v/hen placed in competition with 
each other. We find that if an oat and a mustard plant be grown in 
the same pot with a very limited supply of nitrogen, the mustard probably 
will get nearly all of that plant food and the oat very little. Plants vary 
widely in their ability to cope with each other when placed in keen 
competition. 
* BR9Az;gAi,9, J. B., and Brigos, I^yman J. concentrations of potassium in orthoclase sowtions 
NOT A measure of its AVAii.ABii.iTY TO WHEAT SEEDI.INGS. In JouT. Agr. Research, v. 20, p. 615-621. 
