VEGETATIVE PROPAGATION 19 
the Filmy Ferns of tropical forests, an atmosphere approaching complete 
saturation with moisture is a constant necessity, The Male Fern may 
indeed be accepted as a medium type, showing no special adaptation 
nor susceptibility either to moisture or drought, while structurally it 
shows such characters as are usual 
in average Land Vegetation. 
With very few exceptions Ferns 
are perennials, and in the case of 
the Shield Fern there is no theoretical 
limit to the duration of the individual 
life: in point of fact the plant may 
grow continuously for a long term 
of years, as is shown by the length of 
the stock, and the long succession 
of the bases of leaves of former years 
which may be observed persistent 
upon it in the larger specimens. But 
still it is subject to many vicissitudes, 
which are liable to terminate its exist- 
ence. Some provision must be made 
for the maintenance of the race by 
the formation of new individuals. 
The vegetative mode of propaga 
tion in the Shield Fern is by means 
of buds which appear at a late period 
upon the persistent bases of leaves of 
former years. These develop leaves 
similar to those of the parent, with 
roots which form an_ independent 
system, so that when the progressive 
rotting, which is always advancing 
from the base of the stock onwards, 
isolates the parent leaf from the rest 
of the plant, the bud is in a position 
to subsist as an independent individual 
(Fig. 1, B, Cc). This is merely one Fic. 3. 
example of what is a very common Cystopteris bulbifera (L.) Bernh. A, part of a 
, : leaf with adventitious buds. Natural size. 8, an 
phenomenon in Ferns, viz. the vege- adventitious bud which has fallen off, forming a 
: : Lae ae root. (, an adventitious bud further developed. 
tative propagation of the individual. Bana C’somewhat enlarged. (After Matouschek.) 
The details of the process, such as 
the position and the number of buds, may vary greatly in different 
cases (Fig. 3), but the essential point is the same, that by a purely 
vegetative growth, and without any known cytological complications, 
new individuals may be derived, which are similar in all essentials to 
the parent. Such means of increase are styled collectively under the head 
