XXX 
OUTLINES OF BOTANY. 
cells (190) are formed. These cells separate in layers, the inner ones constituting the 
new ring of wood, and the outer ones the new bark or liber. In most exogenous trees, 
in temperate climates, the seasons of growth correspond with the years, and the rings 
of wood remain sufficiently distinct to indicate the age of the tree ; but in many tropical 
and some evergreen trees, two or more rings of wood are formed in one year. 
212. In endogenous perennial stems (199), the new wood or woody fibre is formed 
towards the centre of the stem, or irregularly mingled with the old. The stem conse- 
quently either only becomes more dense without increasing in thickness, or only in- 
creases by gradual distention, which is never very considerable. It affords therefore 
no certain criterion for judging of the age of the tree. 
213. Flowers have generally all their parts formed, or indicated by protuberances or 
growing cells at a very early stage of the bud. These parts are then usually more re- 
gularly placed than in the fully developed flower. Parts which afterwards unite are 
then distinct, many are present in this rudimentary state which are never further de- 
veloped, and parts which are afterwards very unequal or dissimilar are perfectly alike 
at this early period. On this account flowers in this very early stage are supposed by 
some modern botanists to be more normal , that is, more in conformity to a supposed 
type; and the study of the early formation and growth of the floral organs, called 
Organogenesis , has been considered essential for the correct appreciation of the affinities 
of plants. In some cases, however, it would appear that modifications of development, 
not to be detected in the very young bud, are yet of great importance in the distinction 
of large groups of plants, and that Organogenesis, although it may often assist in clear- 
ing up a doubtful point of affinity, cannot nevertheless be exclusively relied on in esti- 
mating the real value of peculiarities of structure. 
214. The flower is considered as a bud ( flower-bud , alabastrum ) until the perianth 
expands, th c period of flowering ( anthesis ) is that which elapses from the first expand- 
ing of the perianth, till the pistil is set or begins to enlarge, or, when it does not set, 
until the stamens and pistil wither or fall. After that, the enlarged ovary takes the 
name of young fruit. 
215. At the close of the season of growth, at the same time as the leaf-buds or seeds 
are formed containing the germ of future branches or plants, many plants form also, at 
or near the bud or seed, large deposits, chiefly of starch. In many cases, — such as the 
tubers of a potato or other root-stock, the scales or thickened base of a bulb, the albu- 
men or the thick cotyledons of a seed, — this deposit appears to be a store of nutriment, 
which is partially absorbed by the young branch or plant during its first stage of 
growth, before the roots are sufficiently developed to supply it from without. In some 
cases, however, such as the fleshy thickening of some stems or peduncles, the pericarps 
of fruits which perish long before germination (the first growth of the seed), neither 
the use nor the cause of these deposits has as yet been clearly explained. 
§ 4. Functions of the Organs. 
216. The functions of the Root are, — 1. To fix the plant in or to the soil or other 
substance on whicli it grows. 2. To absorb nourishment from the soil, water, or air, 
into which the fibres have penetrated (or from other plants in the case of parasites), 
and to transmit it rapidly to the stem. The absorption takes place through the young 
growing extremities of the fibres, and through a peculiar kind of hairs or absorbing 
organs which are formed at or near those growing extremities. The transmission to 
the stem is through the tissues of the root itself. The nutriment absorbed consists 
chiefly of carbonic acid and nitrogen or nitrogenous compounds dissolved in water. 
3. In some cases roots secrete or exude small quantities of matter in a manner and 
with a purpose not satisfactorily ascertained. 
217. The stem and its branches support the leaves, flowers, and fruit, transmit the 
crude sap, or nutriment absorbed by the roots and mixed with previously organized 
matter, to the leaves, and re-transmit the assimilated or elaborated sap from the leaves 
to the growing parts of the plant, to be there used up, or to form deposits for future 
use (204). The transmission of the ascending crude sap appears to take place chiefly 
through the elongated cells associated with the vascular tissues, passing from one cell 
to another by a process but little understood, but known by the name of endosmose. 
