XXX 
OUTLINES OF 
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 
consequently either only becomes more dense without increasing in thickness, or 
only increases by gradual distension, 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 
regularly placed than in the fully developed flower. Parts which afterwards unite 
are then distinct, many are present in this rudimentary state which are never fur- 
ther developed, and parts which are afterwards very unequal or dissimilar are per- 
fectly 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 confor- 
mity 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 ap- 
preciation 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 clearing up a doubtful point of affinity, cannot 
nevertheless be exclusively relied on in estimating the real value of peculiarities of 
structure. 
214. The flower is considered as a bud ( ( flower-bud , alabastrum ) until the perianth 
expands, the period of flowering ( anthesis ) is that which elapses from the first ex- 
panding 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 albumen 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 germina- 
tion (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 which 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 para- 
sites), 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 retransmit 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. 
