16,5 Espino: Salt Requirements of Young Rice Plants 457 
most important to the human* race. If wheat be the most im- 
portant, then perhaps rice may be the second. Wheat had been 
studied considerably, though much remains to be done with it, 
but rice had received no attention by the newer methods of solu- 
tion culture. Also, various writers had presented evidence to the 
effect that rice differs from wheat and many other plants in that 
rice is able to utilize ammonium as a source of nitrogen. Rice 
also appeared to be well suited to solution cultures. Finally, 
rice is perhaps the most important plant in the writer’s home 
country ; it forms the main vegetable source of food for the great 
majority of the population of the Philippine Islands, and it is a 
very important agricultural crop there, as well as in many other 
parts of the world. Large amounts of it are grown in the south- 
ern and western United States, in Italy, India, Africa, Japan, 
Spain, etc. Lowland rice was selected for the experiments to 
be reported in this paper. 
These studies may therefore be regarded as furnishing some 
contribution to our knowledge of the physiology of the rice plant, 
just as they contribute somewhat to our knowledge of solution 
culture and the mineral nutrition of plants in general. The 
recent intensive study of the mineral nutrition of plants, through 
the employment of the systematic schemes of Schreiner and 
Skinner (1910), Tottingham (1914), Shive (1915), and others, 
has not thus far included the rice plant, but several valuable 
studies of a less extensive and systematic sort have been reported 
for rice. The following paragraphs give a resume of previous 
work on the salt nutrition of rice, with which the writer is 
familiar. 
The problem of the mineral nutrition of rice immediately 
brings up the question of ammonium salts as possible sources 
of nitrogen for plant nutrition. It appears that plants differ 
in regard to their ability to utilize ammonium salts. An early 
publication dealing with this question is that of Bouchardat."* 
He employed culture solutions with several forms of inorganic 
ammonium compounds (“sesquicarbonate,” bicarbonate, sulphate, 
“chlorhydrate,” and nitrate of ammonium) and experimented 
on the growth of Mimosa pudica in these solutions. He con- 
cluded that the ammonium salts used were not only useless as 
sources of nitrogen for the plant employed, but that they were 
highly toxic when supplied in certain concentrations. It was 
* Bouchardat, A., De Taction des sels ammoniacaux sur la vegetaux, 
Compt. Rend. Acad. Sci. Paris 16 (1843) 322-324. 
