16,6 Espino: Salt Requirements of Young Rice Plants 475 
Since the physical, chemical, and physiological properties of 
any complex solution depend (for any temperature, etc.) upon 
(1) the nature of the solutes contained, (2) their proportions 
in the mixture, and (3) the total concentration of the solution,^ 
it is of course necessary, in such a study as this, to make 
comparisons between various nutrient solutions not only with 
reference to the kinds of salts used and their proportions in 
the solution, but also with reference to total concentration. It 
was therefore planned to determine approximately the best total 
concentration (for the growth of these seedling rice plants under 
the non-solution conditions employed for each culture series) 
for each set of salt proportions tested. This means that sev- 
eral different degrees of dilution of each one of the thirty-five 
stock culture solutions already characterized, had to be employed. 
Table 3 shows the different total concentrations that were ac- 
tually used in each case. It also shows the time of year when 
each series of tests was made, as indicated by the dates. The 
different series are set forth under each of the three solution 
types in the order of their total concentrations. 
During the culture period the culture solutions were renewed at 
intervals of three or four days, after the first five days. In 
connection with this sort of work it should not be forgotten 
that a given solution begins to alter in respect to its chemical 
and physical properties as soon as it is brought into contact 
with the plant roots, and that this alteration continues (in un- 
known ways) until the old, altered solution is removed and 
replaced by a fresh one having the standard properties of the 
old one at the start. The supply of the various ions and mole- 
cules at the absorbing surfaces of the roots is of course deter- 
mined by the respective partial concentrations of these in that 
” Different writers state this generalization in various ways, frequently 
from a distinctly not all-inclusive point of view. Some misunderstandings 
as to the nature of the questions involved and considerable resultant dis- 
cussion have occurred in the literature, but the matter is too complicated 
for the present writer to attempt a broad discussion of it here. Especially 
have students of solution cultures given particular attention to these three 
controlling conditions as related to the physiological value of a nutrient 
solution. Whatever may prove to be the most useful way of giving quan- 
titative values to these conditions, it seems quite clear that a plant growing 
in an aqueous solution may be made to grow faster or slower, better or 
worse, by altering any one, or two, or all three, of these characteristics 
of the solution; provided of course that other environmental conditions are 
not altered in a compensating manner, that the change or changes in the 
solutions are sufficiently great, and that the changed conditions are main- 
tained for a sufficient length of time. 
