Xxiv OUTLINES OF BOTANY. 



conformity to a supposed tjpe; and the study of the early formation and growth pf the floral 

 organs, called Organogenesis, has been considered essential for the correct appreciation ot ice 

 afSnities of plants. In some cases, however, it would appear that modifications of development, 

 not to be detected in the very young bud, are yet ot great importance in the distinction ot large 

 groups of plants, and that Organogenesis, although it may often assist in clearing up a doubttm 

 point of affinity, cannot nevertheless be exclusively relied on in estimating the real value oi 

 peculiarities of structure. 



214. The flower is considered as a 6«d (flower-bud, alabastrum) until the perianth expands. The 

 period of flowering (anthesis) is that which elapses from the first expanding of the perianth, till 

 tbe 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, tbe 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 



eed), 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 Eoot are : — 1. To fix tjie 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 place through ' the young growing extremities of tbe 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 organised 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 cif 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. 



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 process 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 is exhaled. 3. The transformation of the residue of the crude sap into the organized 

 substances which enter into the composition of the plant. The exhalation of oxygen appears 

 to take place under the influence ot solar heat and light, chiefly from the under surface of the 

 leaf, and to be in some measure regulated by the stomates; the absorption of oxygen goes on 

 always in the dark, and in the daytime also in certain cases. The transformation of the sap is 

 effected within the tissues of the leaf, and continues probably more or less throughout the 

 active parts of the whole plant. 



219. The Floral Organs seldom contribute to the growth of the plant on which they are 

 produced ; their functions are wholly concentrated on the formation of the seed with the germ 

 of a future plant. 



220. The Perianth (calyx and corolla) acts in the first instance in protecting the stamens and 

 pistils during the early stages of their development. When expanded, the use of the brilliant 

 colours which they often display, of the sweet or strong odours they emit, has not been adequately 

 explained. Perhaps they may have great influence in attracting those insects vrhose concurrence 

 has been shown in many cases to be necessary for the due transmission of the pollen from the 

 anther to the stigma. 



221. The pistil, when stimulated by the action of the pollen, forms and nourishes the voune 

 seed. The varied and complicated contrivances by which the pollen is conveyed to the stiema 

 whether by elastic action of the organs themselves, or with the assistance of wind of insects or 

 other extraneous agents, have been the subject of numerous observations and experiments of the 

 most distinguished naturalists, and are yet far from being fully investigated. Their details 

 however, as far as known, would he far too long for the present outline. ' 



