492 BOTANICAL GAZETTE [DECEMBER 
brane varies with the medium; and that in Rosa canina growing 
in a dry situation the root hair has a stiff pointed apex and that 
the membrane is of lignin, but that in moist air no lignin is 
found. 
Liqguip MEDIUM.—Calcium nitrate-——ScHWARz (20) found that 
15 per cent of calcium nitrate inhibited hair production. KRAUS 
(14) found roots richly haired in calcium nitrate. 
Potassium nitrate—BARDELE (1) found that the root hairs 
on Zea mais, Triticum vulgare, Avena sativa, and Tradescantia sp. 
‘ tend to decrease as the fractional solutions of KNO, increase in 
strength from o.o1 normal to 0.09. 
Salt.—Hix1 (10) found that in Salicornia and Suaeda the root 
hairs can regulate their osmotic pressure in proportion to the 
osmotic pressure of the soil water. 
Bogs.—TRANSEAU (24), working on bog plants, found that 
Larix roots when not surrounded by water develop root hairs 
abundantly. Ruicc (19) used the development of the root hairs 
of Tradescantia as an indicator of the presence of toxins. 
Foop suppiy.—Scuwakrz (20) found that in reducing the food 
supply by removing portions of the endosperm the length of zone 
of root hairs decreased. Snow (21) experimented with Helianthus 
and found that those with the most cotyledon remaining had the 
best formation of root hairs. 
Investigation | 
This investigation was prompted by the fact that the presence 
or absence of root hairs is so often used as an indicator of the 
effect of changed external conditions. That the effect of the 
varying conditions might be known, it seemed well to try to 
determine the varying factors within the epidermal cell of the root, 
as well as the effect of the varying factors without and their recip- 
rocal relations. : 
In order to picture as definitely as possible all the forces which 
might be affecting the epidermal cell, we may consider the aver- 
age epidermal cell as having the form similar to fig. 1. Here 1t 
is seen that on four sides (2, 3, 4, 5) the epidermal cell adjoins 
another epidermal cell, while on the inner side (6) it faces the wall 
