423] S. F. Trelease O25 
Perhaps the main result of this study is, in general, that 
no matter whether we employ (1) the three salts KH,PO,, 
Ca(NO;)., and MgSO, (2) the four salts KH,PO,, 
Ca(NO;)., MgSO,, and KNO,, or (8) the four-salts KH,PO,, 
Ca(NO,),, MgSO,, and KCl, if we use the best proportions 
of the salts in each case we may expect to obtain about the 
same growth. This generalization has an important bearing 
on the whole problem of physiological balance in nutrient 
solutions and furnishes what may be important suggestions 
bearing on our general conceptions of conditional control and 
conditional optima for plant activities. 
THE RELATION OF THE CONCENTRATION OF THE 
NUTRIENT SOLUTION TO THE GROWTH OF YOUNG 
WHEAT PLANTS IN WATER-CULTURES 
By S. F. TRenease 
In these experiments the salt proportions were the same in 
all the different solutions of each series, but the solutions 
differed from each other in total concentration. Three series 
of cultures, all carrsed out at the same time, are considered, 
each series including a concentration range of from 0.5 to 7.0 
atmospheres. A different set of salt proportions was used in 
each series. Six plants were grown in each culture and the 
cultures were in duplicate, upon a rotating table. The ex- 
periment lasted for 32 days, from January 23 to February 
24, 1917, the solutions being renewed every 4 days. 
In the first series the nutrient solutions contained the + 
salts KH,PO,, MgSO,, KCl, and Ca(NO,), in the follow- 
ing relative molecular proportions: 1.000, 0.587, 0.485, 0.341. 
The average dry weight of tops and the average total water 
loss by transpiration, for six plants, are shown in the follow- 
ing table, whch also shows the total concentration employed 
in all three series. 
