22 Birbal Sahni. 
individual. The local reduction or absence of leaves in the latter 
group of forms allows of no doubt that the mode of branching they 
possess is a highly specialized one, and it is most natural to derive 
it from the dichotomous type illustrated by the former group : the 
two extremes are connected by an unbroken series of transitions 
(Fig. 1 C-G, p. 5). 
This conclusion is corroborated by a study of the branching of 
Ferns from the point of view of their vascular anatomy. This 
affords a series of transitions parallel to the above, while indepen¬ 
dent grounds are given for the view that the latter ends of these 
series represent the derivative, the former the primitive condition 
For a resume of our knowledge of the vascular relations of branch 
and stem throughout those Filicales in which branching has been 
described, the reader is referred to p. 9 and Fig. 1, p. 5, 
When the growing apex of a Fern stem divides in preparation 
for branching, the resulting growing points may either both con¬ 
tinue their growth simultaneously, or, as very commonly happens, 
one of them may almost immediately become dormant, while the 
other continues its growth in the direction of the original axis. A 
a third possibility is that the dormancy of one of the growing 
points may be delayed for a variable period of time during which 
the two have been growing together as in the first case. Of these 
three conditions the second will be generally admitted to be 
derived from the first, since it involves a sacrifice of one of the 
branches for the good of the other; while the third condition 
may be considered to be intermediate between the other two. 
An inquiry into the circumstances under which the different 
forms of branching occur shows that the dichotomous types 
correspond to the first of the cases mentioned above, while in the 
extreme monopodial types the branches arise from buds which 
become dormant immediately after their origin, when they were 
still minute. The intermediate types probably correspond with 
the third case. 
There, is no necessary parallelism between the evolution of 
the modes of branching on the one hand, and the evolution of the 
plants themselves on the other : the two processes must therefore 
have been independent of each other. Dichotomy still persists 
among the higher Ferns, while some of the most primitive Ferns 
(Ophioglossaceae) show an advanced monopodial type of branching. 
The monopodial type of branching has been derived from the 
dichotomous by a process of retrogressive evolution in the basipetal 
direction, involving the successive intercalation, at the base of the 
