425] 8. F. Trelease and E. E. Free 



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 KC1 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 S. P. TKELEASE and E. E. 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 x to be 

 best for the production of dry weight of tops In wheat. 'Mie 

 culture jars had a capacity of 250 cc. 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 SLive - Ail 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 daily . . . , , ..... ..... ....... 1.243 



Changed every 3 days 1.012 



Changed every week 1.020 



Changed after 1 week, then every 3 days . , 0.995 



Changed every 2 weeks ....*. ,. ; . 0.780 



Changed after 2 weeks, then every 3 days 1.131 



Changed after 2 weeks, then every week v ...... 0.969 



Changed after 1 month 0.654 



Not changed at all 0.621 



1 Shive, J. W., "A study of the physiological balance in nutrient 

 media." PhysioL Res. 1 : 327-397. 1915. 



