464 Philippine Journal of Science 1920 
Besides the various nitrates and ammonium salts, other forms 
of nitrogen-bearing substances have been tried with rice, but a 
review of the literature on these will not be given here. 
SUMMARY 
From the foregoing review of the more definite contributions 
that have been made toward a knowledge of the mineral nutri- 
tion of rice, it appears that there is good reason to suppose 
that: 
(1) This plant requires the same chemical elements as do 
other higher plants. 
(2) The young plants are not suited to deriving their nitrogen 
from nitrates but thrive very well when ammonium sulphate 
(or probably other ammonium salt, such as the chloride, nitrate, 
etc.) is supplied. 
(3) Older plants are able to derive their nitrogen supply 
from nitrates, but may be able to thrive without the nitrate 
ion when the ammonium ion is supplied at a proper rate. 
None of the points just mentioned is at all well established 
in a quantitative way; much of the experimentation on which 
our present knowledge of these matters is based has been car- 
ried on with field soils, whose various properties were mostly 
unknown, so that (for this reason among others) the results 
of different experimenters are generally not logically compar- 
able. The apparent importance of the relation between nitrate 
and ammonium as sources of nitrogen for young rice plants, 
and of the question regarding the physiological balance for rice 
between the three main kations that are generally required by 
plants (potassium, calcium, and magnesium), makes it appeat 
that more attention needs to be given to the simpler physiological 
aspects of these relations. It was with these points particularly 
in mind that the solution-culture studies on rice seedlings here 
to be reported were undertaken. This work is presented as 4 
beginning only. As is general in such cases, the experimental 
analysis is very incomplete and probably more questions are 
raised than are answered, even in a preliminary way. Ip spite 
of the enormous amount of work needed to obtain satisfactory 
conclusions regarding the physiological problems dealt with by 
the solution-culture method, it seems obvious that the relations 
of any given plant form to the soil in which it is growing W’ 
hardly be understood at all well before the behavior of that 
plant toward free solutions has been rather thoroughly work 
out. Furthermore, if the problems of plant nutrition that are 
