Evolution of Branching in the Filicales. 3 
The morphological nature of the stolons of Nephrolepis has in 
the past been a matter of controversy, 1 but even a superficial 
comparison with other Ferns which are known to possess more or 
less specialized lateral branches to the stem will convince one of 
their true nature ; to Kunze (1849), to Hofmeister (1857) and to 
Mettenius (1861) they were so apparent as specialized shoots that 
the possibility of their being of a different nature did not even 
present itself to them. 
It is, in fact, possible to trace the origin of the highly specialized 
condition in Nephrolepis volubilis downwards through a series of 
transitional stages found in other Ferns, to that in which the stem 
divides at the apex into two approximately equivalent branches. 
This mode of branching is very common among forms with a creeping 
rhizome (Polypodium spp., Davallia spp.), and a forking of the stem 
is occasionally seen even in some erect or semi-erect forms, e.g., in 
Plagiogyria seinicordata. 2 But in many other Ferns, chiefly of erect 
or semi-erect habit, there seems to be a tendency on the part of the 
branches to become modified to serve as organs of vegetative 
reproduction. They undergo a marked elongation in their proximal 
portion, which may be underground and bears only reduced scale¬ 
like leaves, and which in its modified form may be called a stolon. 
The stolon takes a horizontal or oblique course for a longer or 
shorter distance away from the mother axis before it passes over 
distally into the leafy crown. It evidently serves to remove the 
leafy end of the branch away from the mother axis before the 
former can strike root and assert its individuality as a separate 
plant. Velenovsky 3 records in Struthiopteris germanica underground 
stolons as long as three metres; rather similar stolons have recently 
been described by Professor Bower in Thyrsopteris elegans, 
Plagiogyria , etc., while Stenzel long ago drew attention to the 
specialized branches of Alsophila excelsa. The genus Nephrolepis 
indicates a further advance in specialization, since the stolons are 
normally entirely leafless. Moreover, whereas further branching of 
the stolon is rare in the previously mentioned forms (so that usually 
1 For references see the paper just cited, p. 269. 
Among Ferns, structures which in appearance as well as in function most 
closely correspond to the stolons of Nephrolepis are the so-called Auslaufer- 
bliitter (runner-leaves, leaf-runners) of Asplenium obUtsilobum Hk., A. Mannii 
Hk., etc., described by Professor Goebel (Biologisches Centralblatt XXI1, 1902, 
p. 385) and more recently by Dr. Kupper (Flora, 1906, p. 337). There can, 
however, be no question of a homology between the two : the Auslauferblatter, 
as Professor Goebel showed, are morphologically leaves. 
1 Bower, loc. cit., 1910, p. 426. 
* Velenovsky, Vergleichende Morphologie, Prag, 1905, Vol. 1, p. 232. 
