425] 8S. F. Trelease and EB. HE. Free 227 
weight of tops was altered from 1.6 atm. to 4.5 atm. by chang- 
ing the proportions of the four salts used in the first and third 
series. (3) With the salt proportions of the three other 
salts used in the first series, the omission of KCi did not alter 
the relation between growth and concentration. 
THE EFFECT OF RENEWAL OF CULTURE SOLUTIONS 
ON THE GROWTH OF YOUNG WHEAT PLANTS 
IN WATER-CULTURES 
By 8. F. Trevease and HE. EH. Free 
One of the practical problems in work with water-cultures 
is that of the frequency with which the culture solution must 
be renewed in order to obtain the best results. This note re- 
ports experiments in this connection on the growth of young 
wheat plants in the nutrient solution found by Shive* to be 
best for the production of dry weight of tops in wheat. The 
culture jars had a capacity of 250cec. Six plants were grown 
in each jar and each culture was in triplicate. The volume 
of the culture solution was made up to normal by the addition 
of distilled water every 4 days or oftener. The details of the 
technique were the same as employed by Shive. All cultures 
ran 41 days, from January 6, to February 16, 1916. The 
results are given in the following table, in the form ‘of dry 
weights of tops produced, each weight being the average of 
the three parallel cultures. 
Dry Weight. 
grams. 
Changed daly actos ccien tonne hed cats tick damehe ees 1.243 
Changed every 3 days ........0-.. 00: e eee een eeee 1.012 
Changed every week .......... 000 cee eee eee eee 1.020 
Changed after 1 week, then every 3 days ........... 0.995 
Changed every 2 weeks ........0-- cece eee e ees eee 0.780 
Changed after 2 weeks, then every 3 days .......... 1.131 
Changed after 2 weeks, then every week ............ 0.969 
Changed after 1 month .........0.. eee ee eee eee 0.654 
Not changed at all ......---. cece eee eee cee 0.621 
1Shive, J. W., “A study of the physiological balance in nutrient 
media.” Physiol. Res. 1: 327-397, 1915. 
