16, 6 Trelease: The Growth of Rice 625 
of the addition of fertilizer salts, and may involve a determina- 
tion of the changes that the salts undergo after they are added 
to the soil. Such changes may be due to chemical reactions, to 
absorption phenomena, or to both. 
In the present tests, the total quantity of fertilizer was sup- 
plied in a single addition to the soil, made before the plants 
were placed in the latter. Obviously, an adequate investigation 
of this problem will require, also, investigations of the effects 
produced by adding the fertilizer salts at intervals during the 
growth of the plants. 
Since the saprophytic organisms that inhabit the soil play 
a very important part in the chemical changes that take place 
in the soil, a further study must be made of the relation of soil 
bacteria and fungi to the plant reactions resulting from altera- 
tions in the supply of mineral salts. 
The study here reported deals with the effects of additions 
of various proportions of salts containing elements that are 
essential to the growth of plants. Substances that supply only 
non-essential elements are known to produce marked alterations 
in the growth of some plants; and the reactions of plants to 
various stimulating or poisonous substances appear to vary with 
differences in the proportions and concentrations of the nutrient 
salts. Therefore, studies of the kind here discussed must in- 
volve the elements that are likely to produce toxic or stimulat- 
ing effects in the plant. Also, investigations should be made 
into the relation of soil aération to changes induced by altera- 
tions in the mineral salts, with specific reference to the rice 
plant. Moreover, since the effects produced by altering the 
salt supply are very likely to depend upon the acid or alkaline 
reaction of the soil, this phase of the problem must be further 
investigated. 
In the present work, three very common fertilizer salts have 
been employed; one supplying nitrogen in the ammonium form, 
another supplying potassium, and the third the phosphate rad- 
icle. These same nutrients may, obviously, be supplied to the 
plant in available forms by means of many other chemical sub- 
stances besides those used in the present tests, and the plant 
responses may be expected to depend upon the nature of these 
substances.(9) Consequently, studies must be made of the ef- 
fects produced upon the rice plant by supplying these necessary 
mineral] nutrients through the agency of many other substances, 
*See Brenchley,(2) and Free and Trelease.(4) 
