26 BOTANY. [CHAP. i. 



third type, comprising all trees and shrubs, and the 

 great majority of the larger forms of vegetable life, is 

 characterized by the vegetative portion of the individual 

 enduring for more than two years ; such are collectively 

 known as perennial plants, many of which endure for a 

 century or even longer. Under ordinary circumstances, 

 such perennials produce a new reproductive part every 

 season. The above sequence of the life- cycle is not 

 absolutely stereotyped, but can under certain conditions 

 be made to depart from the usual course of development. 

 As an illustration, the common sweet-scented Migno- 

 nette is an annual, but if the flower buds are pinched off 

 as they appear, the vegetative portion persists through 

 the winter and produces an abundance of flowers the 

 following year. 



In the great majority of flowering plants the vegeta- 

 tive portion consists of the three following differentiated 

 parts, each doing a specific kind of work not capable of 

 being done by any other part. 



(r) Root. A true root, as understood botanically, 

 serves to fix the plant in one particular place, a mecha- 

 nical and comparatively unimportant function, the more 

 important and in fact indispensable function being that of 

 supplying the plant with the required amount of water con- 

 taining in solution certain indispensable elements of plant 

 food ; in fact the entire substance of every plant, with the 

 exception of carbon, taken in from the atmosphere in the 

 form of carbonic dioxide by the leaves, is absorbed in a 

 soluble condition by the root. A marked difference be- 

 tween the members of the animal and vegetable kingdoms 

 respectively consists in the power of locomotion or free- 

 dom to move from place to place by the former, whereas 



