OUTLOTES o? 



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 part* 

 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 



ity 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 



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 

 *rom 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 peed, large deposits, chiefly of 

 starch. In many cases such as the tubers ol 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 bo 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. Function* of the Organt. 



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 

 ahiefly 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 leavefi. fluwers, and fruit, 



