iain aaa a Hi dle al 
SS eee 
1905] SNOW—DEVELOPMENT OF ROOT HAIRS 17 
supply of oxygen or on account of rheotropic stimulation by the rising 
water currents was not evident (fig. ro).. The experiment was con- 
tinued by varying the temperatures in the cold jar from 4—26°, giving 
very short hairs on one healthy root and on portions infested .with 
bacteria. Once or twice a tuft of hairs was produced when seedlings 
were changed from cold to warm 
water, due possibly to retardation 
(ASKENASY 2, p. 70;. TRUE 80, p. 
400), but more probably to the more 
rapid adjustment and stretching of 
the epidermal cells in the warm 
water than of the inner cells. KircH- 
NER (29, p. 353) found that 4° C. 
allowed of little or no growth of corn 
roots, while wheat elongated at o°C., 
which may partially account for the 
different hair conditions in the two 
plants in cold water. 
Wheat was planted in a pot of 
garden soil, and the roots allowed 
to come through the bottom and 
pass into warm water, of tempera- 
tures varying from 27-33° C. The 
roots were smooth at 33°, had scanty 
and irregular hairs at about 30°, 
and were more or less hairy at 27°. As this was tried repeatedly 
with the same result, it seems that for wheat, under these conditions, 
30° C. is about the limit of hair production., 
During a period of high temperature in the room, Elodea roots 
growing in soil were observed to be straight and smooth instead | 
of kinky and hairy as is usual. When the temperature fell to the 
normal point, about 21° C., the roots assumed their usual aspect. 
In one case measured, the root growing in ground quartz at 27-34° 
C. elongated 4™™ in five days, and was curved and piliferous. The 
heat was not able under these conditions to suppress hair develop- 
ment. Another plant of Elodea growing in a glass cylinder had 
accumulated a little organic matter in the bottom of the vessel, not 
1o.—Corn roots growing 
in flowing tap water. 
