xliv INTRODUCTION. 



which afterwards unite are then distinct, many are present in this rudimentary 

 state which are never further developed, 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 dis- 

 tinction 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 expanding 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 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 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 parasites), and to transmit it rapidly to the stem. The absorption 

 takes places 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, trans- 

 mit the crude sap, or nutriment absorbed by the roots and mixed with pre- 

 viously 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 tne vascular tissues, passing from one cell to another by a pro- 

 cess but little understood, but known by the name of endosmose. 



218. Leaves are functionally the most active of the organs of vegetation. In 

 them is chiefly conducted digestion or Assimilation, a name given to the pro- 

 cess which accomplishes the following results : — 1. The chemical decomposition 

 of the oxygenated matter of the sap, the absorption of carbonic acid, and the 

 liberation of pure oxygen at the ordinary temperature of the air. 2. A counter- 

 operation by which oxygen is absorbed from the atmosphere and carbonic acid 



