1916] ROBERTS—EPIDERMAL CELLS OF ROOTS 499 
hairs has without the calcium pectate membrane on side r of the 
epidermal cell a third thin layer which is of cutin. It stains red 
with Sudan III and is insoluble in 50 per cent chromic acid. This 
wall r of the epidermal cell of the stem is then chemically different 
and physically of greater rigidity. 
c) The osmotic pressure on both sides of walls 2, 4, 6, and on inside 
of wall 1.—The cortical cell is always plasmolyzed by a solution of 
sucrose which is 0.02M-o.04M stronger than that which plas- 
molyzes the epidermal cell; this indicates that on the outside of the 
wall 6 there is a greater pressure than on the inside; whereas on the 
outside of 2 and 4 there is a pressure equal to that on the inside. 
On the outside of wall r there is a pressure of one atmosphere. 
The variation between the outside and inside pressures of wall 6 
is small, but there is a great variation in the pressures upon the two 
sides of wall r. Table IV gives the osmotic pressure of the root 
hairs of different plants grown under similar conditions. 
TABLE IV 
Plant ee of Plant — peers of 
Re area o.24M sucrose |jLettuce........... 0.30M : 
Amaranthus ....... ie Sea Mustard.......... 0.22M 7 
Batey ee 0.40oM * Nasturtium........ 0. 28M . 
COM seins 0.283M “ OR a ie ei oes, o.22M : 
Com salad i. o.oo 0.283M “* MAAS. sia: taxes 0. 28M 
Cabbage.) 20 is 0.283M =“ Sisymbrium........ o.24M 
Cay ea o.joM * Sunflower......... o.22M : 
Daucus carota...... 24M “ il ii ageil) mertegear era 0.30M 
Wel. 0.24M * 
It will be noted in table IV that all are plasmolyzed by a solu- 
tion of sucrose between o.22M-o.30M sucrose, except barley. 
This is the equivalent of 5.10-7.70 atmospheres. ‘Two facts are 
indicated here: first, that in moist air there is a minimum of differ- 
ence of 4 atmospheres between the pressure upon the inside and 
upon the outside of wall z; and second, that under similar conditions 
there is a remarkably slight variation in the osmotic pressure of 
root hairs of seedlings of different genera. Some roots respond 
more readily than others to the percentages of moisture present 
in the media. Cabbage, alfalfa, squash, and corn show a definite 
