496 BOTANICAL GAZETTE [DECEMBER 
out if it happens to be at the tip of the root hair, but in case it is 
in or near the base of the cell it remains within the root hair. 
The break in the wall is immediately closed as the membrane 
springs back, and it is hard to detect the point of rupture except 
for the position of the escaped protoplasmic contents. The 
younger cells are more likely to 
q burst than are the older ones. 
Fig. 13 (a) shows a radish root 
hair mounted in o. 24M sucrose 
solution; fig. 14 (6) is the same 
; cell after being put in a o.40M 
ots sis sucrose solution. It is to be 
: Fics. 13, 14.—Fig. 13, root hair mounted noted that the walls corre- 
Geib ioe nytenne sponding to 2, 4, 6 are only 
very slightly changed, and 
wall z has decreased, thus showing that even in the same cell the 
physical condition of wall z is unlike that of walls 2, 3,6. In cells 
which do not burst when mounted in water, the surface of wall z is 
increased, as evidenced by a 
swollen tip which may or may 
not assume odd shapes. This 
indicates that wall r of these 
plants has a greater resistance, 
thereby indicating a variation 
in the epidermal cells of differ- 
ent plants, as well as a differ- 
ence in wall z from walls 2, 4, 6. 
It is frequently seen in many 
forms, for example, alfalfa, cab- Fro. xg.—Short root hairs mingled with 
bage, and Verbascum, that short jong ones. 
root hairs are mingled with long 
ones, giving the appearance of younger and older ones being 
together (fig. 15). The difference may be one of time of formation . 
or of a variability in the growth of wall r; at least in these forms 
the length of the hairs is not a grading one as seen in the forms 
usually figured. 
