xlviii OUTLINES OP BOTANY 



is formed towards the end 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 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 pro- 

 tuberances 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 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 mo- 

 dern 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 apprecia- 

 tion 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 doubt- 

 ful point of affinity, cannot nevertheless be exclusively relied on in estimat- 

 ing 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 rootstock, 

 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, be- 

 fore 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 fruit 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 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, 



