536 Reed. — The Value of Certain Nutritive Elements 
research is that they enable the observer to localize processes and products 
of cell metabolism. In consequence, one may expect to learn more precise 
facts concerning the function of the different organs of the cell under 
different conditions. In this respect the study of physiology is put upon 
a cytological basis. A trend in this direction may be expected in the 
future, just as morphology has become so largely a cytological study. 
As more methods are developed by means of which qualitative tests may 
be made upon the cell, the use of such observations will increase. 
Reverting to what has been said concerning the specific role of the 
various elements studied, it may be pointed out that they possess common 
characteristics as well as specific differences. 
The absence of no one essential element seems to be prohibitive 
of spore germination , as a general rule. Of course the growth of the spore- 
lings was never as good in the incomplete solutions as in the complete 
solutions used as controls. In other words, the slight amounts of the 
essential elements in the spore stored as reserve food are sufficient to sus- 
tain growth for a time in an environment which lacks one of the essential 
elements. The resulting germination or growth in any such case is 
modified by characters apparently belonging to individual species. 
The most easily recognizable functions of the essential elements, and 
the most capable of being understood, are those in which the element in 
question is directly utilized in some form in the synthetic formation of some 
organ or substance in the cell. In such processes it is usually not difficult 
to demonstrate that the element in question enters directly into some 
compound or organ of the cell. As an illustration of such a function, the 
role of phosphorus in the formation of lecithin may be given. Unless the 
radical of phosphoric acid be present, there is no way of uniting the glycero- 
fatty acids to the cholin group. Hence, in the absence of phosphates, fatty 
substances accumulate in the cell. The same is true of the reason for the 
necessity of phosphorus in the formation of nucleoproteids. All chemists 
are agreed that phosphorus holds an important position in the grouping 
of the elementary substances which make up the nucleins. The failure of 
the nuclei of Spirogyra to divide in solutions lacking phosphorus can there- 
fore be readily understood, upon the grounds that a necessary element in 
the formation of nucleoproteids was lacking. 
A second class of functions which it has been shown that the essential 
elements are capable of performing, are those in which the element does 
not itself enter into the composition of the end product of the reaction. 
In such cases the essential element may possibly be looked upon as 
a necessary catalyser, or as a dominating factor in bringing about proper 
conditions for the specific reaction to take place. It is probable that the 
greater part of the functions which any element performs in the plant belong 
to this class. 
