1905] SNOW—DEVELOPMENT OF ROOT HAIRS 13 
between the jars, the roots showing individual peculiarities of growth 
under both conditions. In one experiment the general growth in 
length seemed to be a little less in light, accompanied by a slight 
increase in the length and thickness of the hairs. In others no 
difference was noticed. No zonal arrangement was observed, as was 
mentioned by Devaux (11). According to MAcDouGAL (47, 
p- 246) the development of hair upon aerial organs in response to 
light conditions varies greatly, some plants having a tendency to 
decreased hair production in darkness, and others showing no change.* 
A. Seedlings. 
Preliminary experiments showed that the primary roots of seed- 
lings of Triticum vulgare, Zea Mais, Pisum sativum, Cucurbita Pepo, 
Vicia sativa, Helianthus annuus, Brassica alba, and Raphanus 
sativus produced hairs, for a longer or shorter zone, in air or water 
‘regardless of the light conditions. This is attributed by ScHWwaRz 
(75, p. 162) to the abundant food supply, seedlings being in a measure 
independent of external conditions for their existence. 
Seeds of wheat, corn, pea, and squash were sprouted upon moist 
filter paper under illuminated and darkened bell-jars. On plants 
of the same age the hair zones were measured. No decided difference 
was found, though the hair zones averaged somewhat longer in dark- 
ness. The influence of the light was not strong and was probably 
indirect, through its effect upon growth. 
An attempt was next made to compare the increase of surface 
per square millimeter under the two conditions. Seedlings of sun- 
flower, white mustard, and radish were attached to pine bars by means 
of filter paper and rubber bands, as described by NEWCOMBE (55, 
p- 150), and placed in glass jars, one set being illuminated and the 
other darkened. The measurements were taken in all cases, as nearly 
as possible in the zone of best average development, near the top 
of the root. The closeness of the hairs varied in different parts of 
the root, but the average of the numerous counts was probably not 
far from fair. The increase (in square millimeters) per square 
1 In connection with the experiments here reported, the condition of the hairs 
on the epicotyl of etiolated and normal seedlings of Helianthus were compared. In 
the former case the cells were longer and the hairs were not only thus farther separated, 
but fewer cells produced hairs. 
