62 
OF BUDS. 
having their wood arranged in concentric layers, the oldest be- 
ing in the centre of the trunk and the newest forming the outer 
layer ; 2d. such as grow internally ; their wood, instead of cir- 
cling around the first formed substance, being pushed outward 
by the developement of new fibres in the centre of the stem.* The 
first kind of stems, or such as grow externally, may be seen in 
the oak and other forest trees in this climate ; and also in most 
of our common herbaceous plants ; these spring from seeds of 
a peculiar kind called dicotyledonous. The second kind of stem, 
or such as grow internally, is found in plants proceeding from 
seeds called monocotyledonous. 
Fig. 1 1 . A, may give you an idea of 
a monocotyledonous ( endogenous ) 
stem ; you will, by comparing it 
with a woody stem (see plate IX.) 
observe the difference of structure ; 
in the former there are no concen- 
tric lay ers, or vessels of different 
kinds but the structure is homogen- 
eous, consisting of the longitudinal 
fibres which are represented by 
small dots ; the bark does not, like 
that of the stems of dicotyledonous 
plants, consist of its own peculiar set of \essels, but seems not 
separate by any distinct division from the rest of the stem 5 this 
kind of stem is destitute of a proper bark. 
LECTURE VIII. 
Of Buds. 
Most leaves and flowers proceed from scaly coverings called 
buds. The scales envelope each other closely ; the exterior ones 
being dry and hard, the interior, moist and covered with down ; 
they” are also furnished with a kind of resin or balsam, which 
prevents the embryo from being injured by too much moisture : 
and have been known to lie for years in water without injury 
to the infant plant or branch within. 
Linnaeus supposed that buds derive their origin from the 
* These two kinds of stem have by some French botanists been called En- 
dogenous and exogenous ; these words are derived from the Greek ; the first 
signifying to grow within , the second to grow without. 
Buds. 
