Evolution of Branching in the Filicales. 2 1 
dichotomy of the rhizome with a petiole coming off exactly at the 
angle and forming a direct continuation of the axis behind the 
angle. As he pointed out, this case finds the closest analogy in 
Hypolepis tenuifolia, the chief difference being that the branching 
in the latter plant is monopodial, with the leaf more closely related 
to the side-branch. 
Finally, the formation of new plants from adventitious buds 
which are usually confined to the leaves, may also be included 
under branching. In accordance with their origin from minute 
initials, these plants are connected to the parent leaf by a thread, 
like strand which rapidly dilates and becomes elaborated into the 
adult type of stele. This method of branching is probably the 
most recently evolved, but evidently on account of its success as a 
means of rapid propagation, it has already been established in a 
very large number of Ferns, in some cases to the detriment of the 
usual method of reproduction by spores. 
Just as the relation of adventitious buds to primary buds is 
obscure, it would be difficult to relate this latest mode of branching 
to the usual method, in which the branch always springs from a 
bud originally laid down at the growing apex of the mother axis. 
IV. Summary amd Conclusions. 
The most important direction in which the evolution of the 
filicinean branch system has progressed is specialization for 
vegetative propagation. This is only an elaboration of the funda¬ 
mental idea involved in branching, namely, the amplification of 
the plant-body. Subsidary efforts have been made in the direction 
of (a) epiphytism ( Nephrolepis volubilis), ( b) food or water storage 
{Nephrolepis tuberosa, Poly podium Brunei , Hymenophyllum Ulei 
and H. lineare?) 
On taking a bird’s-eye view of the branching of Ferns it is 
observed that the different forms may be arranged in a series 
beginning with those in which the rhizome divides into two more 
or less equal branches, and ending with forms in which the proximal . 
part of one of the branches attains a great length and bears 
either reduced leaves ( Struthiopteris , etc.) or none at all {Nephro¬ 
lepis). This portion, which has been called a stolon, serves to 
remove the leafy apex of the branch away from the mother-axis, 
and to feed it before it establishes an independent root-system. In 
the extreme case ( Nephrolepis) the stolon is capable of producing a 
large number of lateral branches each cf which is a potential 
> Giesenhagen (Berichte, 1909, pp. 331,333) considers the tuberous bodies 
in Hymenophyllum Ulei and H. lineare as insect-galls, but Christ (Geographic der 
Fame, 1910, p. 99) regards them as water-storing organs. 
