The External Form of Plants. 83 
from adventitious buds. There are sometimes a few buds 
which do not break through the bark, but remain dormant 
beneath it, until the other buds on the plant have been de- 
stroyed by unfavourable circumstances such as late frosts, 
when these dormant buds are excited into activity, and 
often preserve the life of the plant. But even while in the 
dormant state they always increase in size ; and form, for 
example, the balls which are found beneath the bark of the 
beech, chestnut, lime, &c. Creeping stems are also sometimes 
developed from these, but more usually from fadventitious 
buds. It is this production of branches on the stumps of 
felled trees, as on oaks and birches, which especially adapts 
them for growth as underwood. The bodies termed dud/bz/s 
or gemme should also be mentioned here. They are stem-buds 
which detach themselves from the plant, and can themselves 
" give rise to new individuals exactly like the parent. They 
are formed, for instance, in abundance on certain species of 
Allium, on the leaves of Cardamine pratensis, in the axils of 
the leaves of Lz/zum bulbiferum, between the scales of bulbs 
(Figs. 121, 122), |and more frequently with Cryptogams, on 
the fronds of ‘viviparous’ ferns, as Asplentum bulbiferum, 
normally on the thallus of Hepaticz, &c. | 
The mode of development of the buds has a great influence on the 
‘habit of the plant. If, for example, the terminal bud of the primary 
stem persists as such, the stem will continue to grow for a long time at 
its apex, as may be seen in the silver fir. Pollarded willows, on the 
contrary, which have Jost their terminal buds, usually form at their 
summit a dense crown of small branches. The dichotomous branching 
of the mistletoe depends on the terminal bud always developing into a 
flower, and the lateral buds into branches. 
‘Buds which persist through the winter are usually pro- 
tected by special organs, the dzd-scales, which are either of 
a membranous or scaly texture. They are either dry as in 
the oak, viscid like those of the horse-chestnut, covered 
with hairs, or smooth. In many cases in which they are 
not specially developed, as in the lilac, they are replaced by 
G2 
