1905] SNOW—DEVELOPMENT OF ROOT HAIRS 33 
to be the only available information on the subject. PERSECKE 
(62a, p. 548) considered the development of root hairs to depend 
upon the amounts of air and water in the interstices of the soil. 
WIELER (86, pp. 223-4), SCHAIBLE (74a), ef al., report an increase 
in the growth of roots as a response to a decreased oxygen pressure. 
ARKER (1a) found that by passing air through water or soil, or by 
diminishing the air pressure above the soil or water, the roots grew 
faster. This he thinks was due not to the greater quantity of oxygen 
but to its greater mobility. The quantity of oxygen necessary for 
growth according to WIELER (86, pp. 213-4) is very small and 
varies with the plant. He found optimum pressure for Vicia 
Faba to be 5-6 per cent., for Helianthus 3 per cent., a retardation 
of growth taking place at o.14-6 per cent. according to the 
to the plant. V6cHTING (82, p. 94) found the roots of potato tubers 
to cease producing hair when the oxygen pressure fell to 3 per cent. 
The growth was slow, therefore the absence of hairs could not in this 
case be attributed to rapid growth of the roots. V6CHTING also found 
(83, p. 132) in experimenting with willow twigs that there was 
sufficient oxygen in water to support life, but not enough for the 
production of new organs, a supply from above the surface being 
needed for the production of roots and shoots. . WACKER (84, p. 110) 
considered that Lupinus albus and Vicia Faba died in saturated 
earth on account of the lack of oxgyen and the presence of harmful 
disintegration products, and believes land plants not to be able to 
supply oxygen to the roots by way of the aerial organs. ScHWARZ 
(75, p. 160) tried to overcome the inimical effects of water upon root 
hair production by passing oxygen through the culture fluid, but did 
not succeed in producing hairs, and came to the conclusion that oe 
factors than lack of oxygen must be considered. 
In the experiments here reported the oxygen content of the medium 
proves itself an important factor. Comparing corn and wheat in 
their ability to produce hair in water, we find that under apparently 
the same conditions the former grows smooth, while the latter pro- 
duces long and abundant hairs. We may be dealing with the indi- 
vidual ability of the two plants to make use of the same amount of 
oxygen in a dissolved form, or with the individual needs of the plants 
for oxygen. Besides, one plant may be better able to supply its roots 
