420 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9, 
Statement of the Problem 
It is clear from the foregoing brief discussion and review of literature 
that the few investigations reported up to the present time which deal with 
top-root growth ratios in plants as they are influenced by nutrient con- 
centrations, give inconclusive results. It has not been possible to say with 
any degree of exactness just which one of several factors has been pre- 
dominant in a given experiment. It has been found that water, tempera- 
ture, light, and shade will influence top-root ratios; but this paper is con- 
fined to the effect of nutrient solutions. Miss Brenchley (3) has recently 
obtained some suggestive results by controlling the temperature factor in 
connection with nutrient cultures, and she shows how very important this 
factor is, especially with reference to the roots. 
In view, therefore, of the scarcity of significant data, the writer has 
undertaken to investigate the influence of certain mineral nutrients in 
altering the ratio of top to root growth in certain plants and to suggest the 
probable mechanism underlying the resulting responses. This is a new 
field for specific investigation, and the solution of the problems involved 
offers much of value to the science of plant physiology, as well as to agri- 
cultural practice. 
To a considerable extent, roots have specific nature and habits of their 
own apart from any characteristics which they may have as co-workers with 
tops for the good of the whole plant; they may be sharply polymorphic, as 
discussed later in this paper, and it has been suggested that they may be- 
have at times as saprophytes when supplied with suitable carbohydrates, 
living at the expense of tops. 
Materials and Methods 
Since these experiments were concerned with the effect of nitrates, a 
prerequisite at the outset was to devise a solution which would allow a wide 
variation in the nitrate ions without affecting very much the other essential 
elements necessary for favorable plant growth. One has ordinarily a wide 
choice in the selection of a nutrient solution; the general point of view, as 
gathered from a study of the solutions used by the various investigators 
and from their statements, is that there is no "best solution" nor specific 
ratio of ions or elements which will insure an optimum yield of plants under 
all conditions. Solutions, as mentioned already, which give optimum yield 
of roots, may not and often do not give optimum yield of tops, if by "op- 
timum" we mean greatest green weight or dry weight. 
It has been shown that, provided the total supply of mineral nutrients 
is adequate, the toleration of plants may extend over wide limits without 
significant falling off in yield. 
The problem of varying nitrate ions for the present study without 
affecting greatly the other components was met by combining calcium 
