AMERICAN 
JOURNAL OF BOTANY 
Vol. I X October, 1922 No. 8 
STUDIES OF THE MECHANISM OF THE PHYSIOLOGICAL 
EFFECTS OF CERTAIN MINERAL SALTS IN ALTER- 
ING THE RATIO OF TOP GROWTH TO ROOT 
GROWTH IN SEED PLANTS 
Thomas Wyatt Turner 
(Received for publication December 14, 1921) 
Introduction 
Very few researches are recorded in the field of plant physiology which 
deal specifically with top-root growth ratios in plants and with the factors 
that may alter such ratios. In attacking this problem, great diflficulties are 
unavoidably encountered because of the complexity of the medium in 
which experiments with roots must always be carried on. From the stand- 
point of physical chemistry, our knowledge as to reactions between plant 
roots and the mineral nutrient solutions in which they may be growing is 
not much more perfect than that of reactions among plant roots, soil par- 
ticles, and soil solution. 
The scientific plant grower as well as the physiologist would be greatly 
aided in their respective fields if there could be furnished a more exact 
knowledge of the interrelations between the aerial and the subterranean 
plant parts: as to how intimately interdependent these members are, and 
also to what extent and under what conditions either may behave inde- 
pendently of the other. 
Getting results of physiological value in respect to this problem from 
investigations with woody plants is a slow and tedious undertaking, yet 
the field of horticulture and pomology through its numerous experiments in 
pruning and grafting contains much valuable material which clearly in- 
dicates the varying relationships of tops and roots under varying conditions 
of nutrition and treatment, as well as the necessity of more exact physio- 
logical investigations seeking to get at the causes. The fertilizer problem 
will not be solved either from a scientific or from a practical point of view 
until more definite information is obtained as to how the particular fertilizer 
used affects the plant roots, or as to how to localize the effect of a particular 
treatment in the desired organ. 
The investigations discussed in this paper are concerned chiefly with 
the effects of nitrate ions upon the relative behavior of tops and roots in 
[The Journal for July (9: 339-413) was issued August 30, 1922]. 
