1916] ROBERTS—EPIDERMAL CELLS OF ROOTS 501 
c) The osmotic pressure on both sides of 1, 2, 4, 6.—The only wall 
on which the osmotic pressure may be made to vary at will is on 
the outside of wall zr. Radish seedlings were grown in sucrose 
solutions of increasing concentrations in order to vary the osmotic 
pressure on the outer wall. The results obtained as the average 
of several series are given in table VI. 
TABLE VI 
D Length hair in | Osmoti bereean onmed 
Gown ta Diameter root in otic een : _ 
in 1/too mm. 1/100 mm. pressure a age pack a 
PP 6 og Oo gs canes OOO NI i awe ae 28 
WE o's be eres en 40 50 38 38 
©.02 molecular sucrose ..... 40° 30 42 40 
0.04 * eee a - 40 20 42 38 
0.06 . SO haa 40 40 42 36 
oe." eu es 40 50 49 32 
°.I0 . es ae 20 20 40 30 
0.12 - a er as 40 60 42 3° 
0.14 = eo hela 55 60 44 39 
0.16 * gee ee 30 40 48 32 
0.18 * ng ree, PC ae ° pe) ° ° 
0.20 . Oa ie dey phn ° 20 ° ° 
oan -* Ws hess 20 10 50 38 
0.24 . a eon Se 30 10 65 41 
0.26 , iit Sot 30 20 60 34 
0.28 co Te ere 50 20 65 37 
oan." Res 40 40 65 35 
0.32 . Ware onus 30 Be) ° : 
0.34 i Wee es 40° 40 7° 3 
0.36 e Pies ey 15 10 75 39 
o.48°: * ge ae 20 10 65 27 
0.40 . se 30 20 ° ° 
0.42 . - 20 15 A) oi 
ou * waa tes 50 15 7o 36 
0.48 a: ie ees 70 TS 3 et 
0.48 " Soe aaa ° ° 
°. $2 8 a seeden 50 20 80 28 
0.60 x a a SS 50 ° go 3° 
0.65 ng aa eee 50 be) 100 35 
It is seen that as the concentration of the media increases the 
osmotic pressure of the root hair increases almost in direct propor- 
tion. Thus the root hair maintains an osmotic pressure from 4 to 6 
atmospheres above that of the medium. 
Differential media.—The effect of different media on the two 
sides of a seedling root was determined. Petri dishes were filled 
with the solutions, seeds were attached to the edge, and the roots 
