THE ROOT-SYSTEM OF IMPATIENS ROYLEI. 513 
raised portions may develop into new apices, and the larger the projection, 
the more likely it is that a fresh apex will result. It is probable that, in the 
aerial adventitious roots referred to, exposure alone is sufficient to account 
for the injury to the delicate tissues of the root-tip and thus lead to the 
characteristic response. 
Q ©, го 
Fie. 20.—a-g. Sections through adventitious root showing development of rootlets and of 
two root-apices as the result of decapitation. A-g. Sections through a root 
showing the development of rootlets resulting from a severe oblique decapitation. 
Text-fig. 19 d-j show another example of apparent dichotomy, but in this 
case the injury passed a little way down one side of the root, thus breaking 
up the vascular ring on that side and causing cork formation. 
Text-fig. 19 -o show successive transverse sections of such a specimen as 
is shown in text-fig. 18e. Here, four projections of the plerome have led to 
the division of the main root into four. In this case one small rootlet is given 
