24 BOTANICAL GAZETTE [yuLY 
C. Wounding. 
SCHWARZ (75, p. 158) was not able to cause hair formation by 
cutting off the roots 2-10™™ from the tip, nor by burning the tip 
with caustic. In my experiments the results were various according 
to the conditions. If the wound were not of sufficient depth to retard 
growth, if it were beyond the elongating zone, or if the plants were 
grown in warm water, no swelling or hairs appeared; -otherwise 
hairs were produced. Thus in corn seedlings the tips of primary 
roots were pinched off about 1™™ from the tip. One showed hairs 
upon the swollen tips; another sent out a tuft of hairs and then 
grew smooth. In the latter case the wound was not of sufficient 
depth to more than slightly retard the growth. Of roots cut and 
burned, several showed hairs, the burned ones curving; several 
simply stopped growing and produced laterals; while others showed 
no effect. The cut tips of corn roots growing in air and producing 
short hairs became slightly swollen in twenty-four hours, and long 
hairs appeared above the cut. Both in light and darkness hairs 
were produced above the cut, whether the swelling appeared or not. 
This may have been due to the appearance of new hairs among the 
old ones, or to the stimulated growth of some of the old hairs, but 
more probably to the retardation of the zone in process of formation 
when the operation was performed. Drvaux (10, p- 308) states — 
that new hairs‘may appear among the old ones, but appearances : 
which might be interpreted in that manner might be due to arrested 
development of some of the hairs. This would be difficult to | 
decide, unless hairs were actually seen to originate between others 
(fig. 2). SCHWARZ (75, p. 165) and HABERLANDT (75, P- 1874 
state that hairs are always produced in acropetal succession. 
D. Medium. 
SACHS (71, p. 410) found that roots of land plants grew more — 
rapidly in soil than in air or water, and his results have been con- | 
firmed by WACKER (84, pp. 109-11 5). The latter, however, foun 
‘that in slimy soil the growth was retarded more than in water, and 
the denser the material the slower the growth. PFEFFER (66, p. 320 
says the rate of growth is not affected by the density of the medium 
roots growing as rapidly in fluid clay as in water. These conflicting 
