36 BOTANICAL GAZETTE [JULY 
measurements of epidermal cells of roots grown under conditions 
producing hair is likely to be less than a similar average from the roots 
of the same species grown under conditions unfavorable for hair pro- 
duction. In the same root the average length of piliferous cells is less — 
than that of smooth cells. ScHwarz makes the significant statement 7 
(75, p. 177) that if in the roots of Elodea and Nuphar the short cells © 
do not produce hairs, in time the difference in length is lost, thus | 
indicating that the short cells stretch out if they do not grow into 
hairs. LEAvITT (41, p. 300) reports the same condition for Nym- — 
phaea dentata. In Sagittaria Eatoni (LEAVitT 41, p. 292) and Phrag- | 
mites (KRAEMER 34, p. 22) the difference in size remains when no 
hairs are formed. The various statements concerning the condi- 
tion of the root epidermis and the appearance of root hairs in the 
latter form are far from clear. | 
From jig. 4 it will be seen that in corn root the origins’ of thell 
hairs appear quite near the tip of the root, where the cells are isodia- 
metric (OLIVIER 58, p. 72). The statement that hairs appear in the | 
zone where the cells have undergone considerable extension (LEAVITT _ 
41, p. 274) or are just ceasing to elongate (DEBARY 3, p. 57) does : 
not seem to be true generally. A probable explanation of the con- — 
ditions observed by these authors is that the growth energy of the cell, — 
after elongation has ceased, finds its expression in the rapid growth — 
of the young papilla, which then takes on the typical appearance of 4 
a hair. By marking the roots of a series of corn seedlings growing — ‘ 
in moist air, hairs visible to the eye were in several instances observed 7 
in the zone of elongation. 2 
As mentioned above, in the plants studied there was no evidence 4 
el ied gees ee een 
reports in some ieiber of the Gramineae the whole epidermis t¢ to 
be piliferous. If each cell of the root epidermis is able to produce | : 
a hair, what prevents such an outgrowth from taking place? 
are turgescent and orhiok nearly equally. Fig. 5isa ae 1 
section from a root of this water type. If, on the other hand, we | 
