1905] SNOW—DEVELOPMENT OF ROOT HAIRS 15 
WENT (85, p, 8) found in aerial roots that light was not favorable 
to hair production except in very damp air, which makes it appear 
that with aerial roots in general moisture is of much more importance 
for hair development than light (PFEFFER 64, p. 130).3 
When seedlings of corn were allowed to send their roots through 
the bottom of the pots into moist chambers, one darkened and one 
left in diffuse daylight, little difference was observed between them, 
some roots in light producing more hairs and some less than those 
in darkness. There seemed a slight tendency for the hair to be 
thicker in light. Mer (51, p. 584) found variation in the appearance 
of hairs on the different roots in the same culture, and considers 
“cette inégalité d’apparition des poils dans un méme milieu est bien 
propre & montrer que leur développement est étroitement lié a la 
constitution particulitre de chaque radicelle.”” No zonation such 
as DEvAUX (11) reports was noted in these cultures. In some 
cases, wheat, corn, and sunflower produced hairs in irregular zones, 
which however could not be traced to the effect of light and darkness. 
Any one of the many causes which may result in irregular growth 
might have been responsible. Where there is any effect on the 
development of root hairs produced by light, it appears from the 
above consideration to be due to the indirect effect upon growth. 
It does not appear to have the direct retarding influence as found 
by V6cuHTING in the case of the growth of willows and the develop- 
ment of new organs (83, pp. 152-162). 
TEMPERATURE. 
The effete of high and low temperatures upon growth has been 
studied by many investigators (64, pt. 2), with the general result that 
increase of temperature favors growth on account of greater or 
more rapid absorption. KIRCHNER (29, pp. 353-355) reports 
growth increased by high temperatures; NEMEC (54a) found longer, 
thinner cells in warm water than in cold; Popovict (67, pp. 37, 88) 
states that high temperatures (33° C.) diminish the zone of elonga- 
tion, while low temperatures, just above the germination minimum, 
increase it, although the total growth is less. KosaROFF (328) 
3 For numerous instances of hair ans on aerial roots touching a support, 
See the bibliography in WeENT’s paper. 
