242 
PHYSIOLOGY. 
BOOK II. 
constitution : as in annual and herbaceous plants, and in those 
the leaves of which are opposite and not alternate ; but all 
the more essential circumstances of their growth are the same 
as those of the apple tree. 
If we reflect upon these phenomena, our minds can scarcely 
fail to be deeply impressed with admiration at the perfect sim- 
plicity and, at the same time, faultless skill with which all the 
machinery is contrived upon which vegetable life depends. A 
few forms of tissue, interwoven horizontally and perpendicu- 
larly, constitute a stem ; the development, by the first shoot 
that the seed produces, of buds which grow upon the same 
plan as the first shoot itself, and a constant repetition of the 
same phenomenon, cause an increase in the length and breadth 
of the plant; an expansion of the bark into a leaf, within 
which ramify veins proceeding from the seat of nutritive 
matter in the new shoot, the provision of air-passages in its 
substance, and of pores on its surface, enables the crude fluid 
sent from the root to be elaborated and digested until it be- 
comes the peculiar secretion of the species ; the contraction of 
a branch and its leaves forms a flower ; the disintegration of 
the internal tissue of a petal forms pollen ; the folding in- 
wards of a leaf is sufficient to constitute a pistil ; and, finally, 
the gorging of the pistil with fluid which it cannot part with, 
causes the production of a fruit. 
In hot latitudes there exists another race of trees, of which 
Palms are the representatives ; and in the north there are 
many herbs, in which growth, by addition to the outside, is 
wholly departed from, the reverse taking place ; that is to say, 
their diameter increasing by addition to the inside. As the 
seeds of such plants are formed with only one cotyledon, they 
are called monocotyledonous ; and their growth being from 
the inside, they are also named endogens. In these plants the 
functions of the leaves, flowers, and fruit are in nowise dif- 
ferent from those of the apple ; their peculiarity consisting 
only in the mode of forming their stems. When a monocoty- 
ledonous seed has vegetated it usually does not disentangle its 
cotyledon from the testa, but simply protrudes the collum and 
the radicle ; the cotyledon swelling, and remaining firmly 
encased in the seminal integuments. The radicle shoots 
