4i6 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9- 
certain plants. There has long been a well defined impression that nitrates 
check the growth of roots; whether this supposed checking is the result of 
the action of the salt ions directly upon the roots, or whether the effect is 
brought about indirectly because of a much more stimulating effect of the 
salt ions upon the aerial portions of the plant, has been left, in a large 
measure, unanswered. 
Status of the Problem as Presented in the Literature 
Moeller (19) was one of the first workers to call attention to the dif- 
ference in ratio between tops and roots of plants as they grew in solutions 
of different concentrations. The more dilute solutions which he used were 
such that they brought about, as he states, dwarfing of the plants growing 
in them. It would seem, therefore, that his results should be attributed 
more to starvation effects than to any definite consequence of the concentra- 
tion as such. He found that weight of tops was five times that of roots in 
the normal plants, while in the dwarf cultures the top weight was only 
twice that of roots. The root systems of the dwarf plants, however, were 
absolutely smaller than those of the normal. 
In- 1906, Livingston (17) worked upon the relation between roots and 
tops in wheat. He grew his cultures in soil, using a "poor" soil from 
Takoma Park, Md., as the basis. In some of his experiments he used the 
"poor" soil untreated, in others he added stable manure ranging from 
5,000 p. p.m. to 50,000 p.p.m.^ He drew the conclusion from his work that 
variation in tops is correlated with the number and length of lateral roots. 
He found that poor soil inhibits growth of lateral roots and also brings on 
a premature aging of the cortical cells, both of which conditions inhibit the 
intake of water. He thus explains the dwarfing of tops in his "poor "-soil 
plants largely on the basis of an inadequacy of water. Soil cultures are not 
wholly comparable to water cultures, yet the poverty of certain mineral 
nutrients in water cultures will bring about a lowered ratio of tops to roots, 
as Livingston found in his "poor "-soil experiments, and in such case there 
is no evidence that a deficiency of water supply is a factor. In a soil devoid 
of nutrients, there would be, undoubtedly, retardation of the growth of 
both tops and roots. 
Harris (12), working in 191 3 at Cornell University, sought to determine 
to what extent the ratio of tops to roots in certain plants is affected by 
moisture, plant food, and age. He grew plants in aqueous extracts of soil 
and in sand in which moisture and fertilizer were controlled. His results 
indicate that all three factors considered in the experiment influence the 
ratio of tops to roots in a positive way. His experiments with plants 
grown in solution and in soil, while in no way conclusive as to the relative 
parts played by moisture and fertilizer in altering ratios of tops to roots, 
are very suggestive. A brief table (table i) of some of his results will bring 
out very well the conclusions. 
^ P. p.m. — parts per million. 
