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. 



Liquid 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 — Bardell (i) found that the root hairs 

 on Zea mais, Triticum vulgare, Avena sativa, and Tradescantia sp. 

 tend to decrease as the fractional solutions of KN0 3 increase in 

 strength from 0.01 normal to 0.09. 



Salt. — Hill (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. RiGG (19) used the development of the root hairs 

 of Tradescantia as an indicator of the presence of toxins. 



Food supply. — Schwarz (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 Helianthns 

 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 it 

 is seen that on four sides (2, 3, 4, 5) the epidermal cell adjoins 

 another epidermal cell, while on the inner side (<5) it faces the wall 



