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pear, and fertile and poor spoils grow plants of equal vigor and feeding capacity. 
When the soil is removed from the tumbler and dipped in hot paraffin to cut off 
the supply of air, there is no longer any tendency for the roots to come to the sur- 
face as they can get no air there, and, with a soil so prepared by the use of hot par- 
affin after the plants are started, the characteristics of the soil then appeared as 
shown in the transpiration. 
It appears that with soils of this character you can get better effects, you can 
improve the functional activities of the plant, either by giving it more air — as by 
growing it in that small pot, under the conditions described — or by the use of ferti- 
lizers and chemicals, which may have the effect on the plant to protect it from this 
hardening or the formation of cork, or whatever physiological effect it maybe which 
limits and controls the functional activities and feeding capacity of the plant. 
It would seem possible, therefore, to develop a method along these lines by which 
the fertilizer requirements of a soil can be closely determined, as nearly and perhaps 
more certainly than they could have been by the older methods of chemical analysis 
that we all have long hoped would be able to solve these same questions. It will never 
be possible, however, by this or any other method, to tell what can be advantageously 
used on a soil during a subsequent year. We know that in certain seasons potash 
will do good; in other seasons phosphoric acid will do good. The character of the 
season probably has a great effect in modifying the action of these salts in solution 
upon the physiological activities of the plant. It will never be possible to tell what 
any particular soil will need unless we know what the character of the season is 
going to be. The only thing we can hope to do will be to tell what that soil will 
respond to under certain conditions under which we can place it, and then, I pre- 
sume, take our chances on having the results come out as we expect them to do 
under field conditions. 
It seems probable, therefore, that we shall be able to develop a method that can 
be used in the field for the study of the condition of the soil as related to the growth 
and functional activities of the plant, and that we shall be able, possibly, to determine 
how far we can change them by methods of aeration or by methods of physical 
treatment; but certainly, I think, it is going to be possible for us to determine what 
fertilizers can be used to correct these difficulties under the conditions of our experi- 
ment, which is a long way ahead of anything that we have at the present time. 
There probably will be a great deal of criticism, a great many questions to be asked, 
a great many questions to be solved, but I believe this matter can be put on a proper 
basis and can be thoroughly worked out. One of the questions to be asked is: What 
is the reason the different forms of phosphoric acid produce different results as to 
plant growth? Now, it seems to me that is easily answered if we consider that the 
insoluble phosphate of lime and the reverted phosphate and the acid phosphate of 
lime are different salts. They are altogether different salts and have different prop- 
erties — have different properties in solution, have different effects on plants. It 
seems to me it can not be the amount of phosphoric acid that these various salts add 
to the soil. The solubility of calcium phosphate is about six parts of lime in a mil- 
lion parts of water. That is strong enough for plants to grow in. It is as strong as 
many of our soil solutions, so that the plant can get from the solution of the so-called 
insoluble calcium phosphate enough phosphoric acid for its needs. The effect of 
these different forms of salts appears to us to be due to some external influence they 
have upon the conditions of the roots, so that the roots may make a more or less 
healthy development, and will present more or less of an absorbent surface. You 
understand that the tips of the roots, which absorb the moisture, do not continue in 
this state for an indefinite time, but for only a short time. The tip of the root is 
active but for a few days at most in ordinary soils. After it has existed for that 
length of time it hardens and becomes nonabsorbent to a great extent, and the tip 
grows out and presents constantly a new surface for the absorption of its moisture 
and food material. This is another question that I might have referred to further 
back in my talk. The fact that these tips are constantly growing makes it relatively 
unimportant for us to know how much water the soil can deliver at a given point. 
If the soil were delivering at the roots so many grams per day, we need not assume 
that it could deliver this quantity continually until the water supply was exhausted, 
as there would be no object in delivering water at that point, for the root is going 
to grow and get into another portion of soil where it will get a fresh supply of water 
and of food. 
Without going into a great deal more detail than our time will permit, I think I 
have given a statement, brief and to the point, of the facts as we have developed them 
so far governing the fertility of the soil as dependent on this chemical question. It 
seems to be not dependent upon the amount of material so much as upon the char- 
acter of the material and the effect of that material upon the absorbent power of the 
plant. That we can influence this is unquestionable, because the experiments are 
