266 BOTANICAL GAZETTE [ APRIL 
meant that the whole of the apical meristem passes into the 
meristem of the branches, this is not a case of true dichotomy. 
At an early stage the meristems of the two branches become 
definitely outlined, but between them, retaining a central apical 
position, there remains a portion of the original meristem. This 
true apical meristem 
gives no indication of 
continuing the axis, and 
does not even begin to 
form bundle elements, 
but soon becomes indis- 
tinguishable, and the 
later stages of the root- 
lets show what seems 
to be a real dichotomy. 
The conclusion is that 
this is a case of apparent 
dichotomy in which the 
meristem of the main 
axis ceases to function 
almost as soon as the 
meristems of the two 

Fic. 1.— Habit of tubercles; nat. size. branches are differenti- 
ated from-it. It may 
be of interest to note that some of the tubercled rootlets do not 
branch, and that the normal rootlets do not show even an appa- 
rent dichotomy. 
A transverse section of one of the tubercles (fig. 2) shows a 
central vascular cylinder like that of the normal root, and a very 
thick cortex interrupted about midway by the greenish algal 
zone (jig. 2,a). The inner mass of cortex consists of ten or 
twelve layers of cells. The outer region is more differentiated, 
consisting of elongated parenchyma cells next to the algal zone, 
a zone of roundish cells with small intercellular spaces, a layer 
of cork cambium, and two layers of corky cells. 
In longitudinal sections the algal zone is seen to extend from 
