1905] SNOW—DEVELOPMENT OF ROOT HAIRS 27 
47, p- 64; et al.) the attenuation of the axial members of etiolated 
plants, where it occurs, is due, in part at least, to a lack or diminu- 
tion of transpiration. A greater proportion of water in etiolated 
plants is reported by MacDoucalL (47, p: 64), PALLADIN (60a), 
JUMELLE (28, p. 386), ef al. 
Whether turgor is the ‘cause or the result of growth, elongation 
of a cell is directly connected with its turgescence, greater water 
content producing greater elongation. Besides instances of etiolation, 
this is shown by the curling of roots which rest on the surface of 
water (SACHS 71, pp. 398-9); by the rounding up of filamentous 
algae (LIVINGSTON 43, Pp. 308; 44, pp. 310-312) and of fungi 
(RAcIBORSKI 68, p. 111) upon withdrawal of water by osmotic 
solutions, and by the tendency of cells to stretch radially from loss 
of water by transpiration (KOHL 31a, p. 297)... The more turgid 
a cell becomes, therefore, the greater the tendency to stretch in a 
longitudinal direction. The water content of the root cells may be 
affected by changing the moisture content of the air, by altering the 
water content of the soil, or by surrounding them with solutions of 
higher osmotic pressure. 
A. Transpiration. 
It is well known that aerial transpiration favors the ca 
of hairs upon aerial organs, WoLLNY (89, pp. 418-435) reporting an 
increased number of piliferous cells by count. On the other hand, 
some hairy-leaved plants grown in an aquatic habitat become smooth 
(CosTANTIN 8, p. 40), and many have noted the absence of hairs 
on roots in water. Experiments to determine the effect of transpi- 
ration from leaves upon the development of root hairs gave negative 
results. Roots grown in saturated air at various temperatures 
showed few or no hairs, and any change that reduced the moisture 
content favored their development. Control plants showed that 
the temperatures used could not alone produce the results. 
: B. Saturated soil. 
For these experiments corn and wheat were chosen because the 
former is very sensitive to the inhibitory effect of water, and wheat 
readily develops hair in that medium. 
