272 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9 
seedlings were reared in flowing tap water tempered to about 25 degrees C. 
This water is drawn from Lake Mendota and has the following composi- 
tion in p. p. m.:^ K 2.2, Ca 19.8, Mg 21.6, P undetermined, S 5.0, N i.i, 
pH approximately 7.5. It supports excellent growth of wheat seedlings, 
especially as regards the root s^^stems. Three duplicate cultures of 5 
plants each were mounted in wide-mouthed jars of about 480 cc. capacity 
(Mason pint jars) through which the nutrient solution flowed continuously 
at the rate of about 4 liters per jar daily. The nutrient solutions of three 
other similar cultures were renewed every third day. Finally, three dupli- 
cate cultures were grown in jars of about 240-cc. capacity and received fresh 
solution every third day. These cultures grew from February 14 to March 
I, 1 92 1. No climatic records were taken in the greenhouse during this 
period. The data of yields are assembled in table 2. 
Table 2. Influence on Growth of Proportion of Plants to Nutrient Solution 
Form of 
Renewal 
Capacity of 
Culture Vessel 
Average Length 
Average Dry Weight 
Root? 
Tops 
Roots 
Tops 
Cc. 
Mm. 
Mm. 
Mg. 
Mg. 
Continuous 
480 
121 (5)* 
Not 
114 (II) 
232 (13) 
3-day 
480 
150 (8) 
measured 
130 (16) 
338 (23) 
3-day 
240 
121 (5) 
140 (12) 
353 (45) 
* Average departure from mean. , 
On the basis of dry weight of plants produced, the method of inter- 
mittent renewal was superior to that of continuous replacement. These 
results are not in agreement with those of Trelease and Free (20), but the 
rates of continuous renewal, and probably also the climatic complex, dif- 
fered in the two tests. 
Conditions generally associated with injury from acid, such as darkening 
and withering of leaf tips, were apparent in all the cultures at the time of 
harvesting. They appeared earliest and most severely, however, in the 
cultures whose solutions were continuously renewed. We interpret this 
difference as due to the ability of the plants to reduce the hydrogen-ion 
concentration when the solutions were renewed at intervals, as demonstrated 
by Hoagland (7, p. loi), Toole and Tottingham (19) and Duggar (3, pp. 11, 
15, 19). It may be noted that growth was most uniform in the cultures 
whose nutrient supply was continuously renewed. These results support 
the assumed importance of continuous renewal of nutrient solutions, or 
equivalent treatment, so that the plant may be subjected continuously to 
a constant composition of the nutrient medium. 
2 Compiled from data of the Wisconsin Geological and Natural History Survey and 
of the State Hygienic Laboratory, , 
