268 
Birbal Sahni. 
uniformity of behaviour of the stolons in each individual pot), some 
of the vertical stolons in pot 3 and some in pot 2 ( N . todeaoides) 
were artificially propped up on wooden sticks so as to remain 
horizontal. After a week or ten days the bent tips of the stolons 
in each case showed evident signs of re-adjusting themselves to 
their former directions of growth ; and in pot 2, some new second¬ 
ary stolons which had developed during this period on portions of 
the primary stolon distal to the bend, grew vertically downwards 
as expected. 
Case 2 may at first seem inexplicable, and it was the one most 
frequently met with, but perhaps it can be interpreted in the 
following way. If it were not for the proximity of the moist table 
on which the pot was placed, the stolons would probably tend to 
grow approximately in a horizontal direction, till they become too 
long, when their weight would come into play. The presence of 
the moist substratum, however, calls forth a positive hydrotropic 
response. The oblique position taken up by the stolons would thus 
be a compromise between two tendencies, the horizontal and the 
vertical. 
No marked geotropic response seems to be exhibited by the 
stolons. The case of the vertically-growing stolons in the hanging 
plant mentioned above is probably to be explained, mainly at least 
by the weight of the long stolons. Any geotropism, if present, must 
be weak. According to Lachmann, 1 the stolons produced on the 
underground region of the principal axis are geotropically less 
sensitive than the roots of most ferns. Sperlich who in 1906 2 
expressed the belief that the subterranean stolons of Nephrolepis 
are positively geotropic, in 1908 3 withdrew this view in favour of 
positive hydrotropism. 
In the later paper just cited (p. 356) Sperlich raises the 
question whether Nephrolepis stolons are also sensitive to contact 
stimuli. The curious way in which the stolons pass close over the 
edges of the pots (see p. 267) is rather suggestive, but Nephrolepis 
volubilis affords a case which reminds one strongly of the tendrils 
of higher plants (Text-figs. 1 and 2). In Text-fig. 1, a portion of 
the long primary stolon (p) is shown bearing several lateral plants 
( x ), while surrounding the points of origin of these lateral plants 
are seen the close coils of the tendril-like stolons, two of which are 
1 Lachmann, Contributions, etc., p. 150. 
2 Sperlich, Flora, 1906. 
* Sperlich, Flora, 1908, p. 354. 
