bb WHY PLANTS GROW, 



271. Some Forms and Changes of Vegetable Matter. It may be used at once, or it 



may be stored up until it is wanted. In annual herbs, as already explained (68), 

 .nearly all of it is used for growth or for blossoming, as fast as it is made. In 

 ibiennials, like the Beet, Carrot, and Turnip (70), a great part of it is stored 

 up somewhere, generally in the root, and used the next year. In such perennials 

 as the Potato, a part is laid up in the tubers (which are all of the plant that 

 survives the winter), to begin a vigorous growth the next season. In shrubs and 

 trees a part is annually deposited in tlic newest wood and bark, to be used for de- 

 veloping the buds the next spring. In all, a ])ortion is deposited, as we know, 

 sometimes in the fruit, always in the seed, for the use of the embryo or new plant, 

 ar, the beginning of its growth. 



272. When vegetable matter is laid up for future use, a large part of it is gen- 

 erally in the form of starch. Nearly the •v\hole bulk of a potato, or of a grain of 

 corn, is starch. This consists of little grains which arc like mucilage solidified, and 

 they may be tui-ned into mucilage again. When the plant takes up a deposit of 

 starch into its system, as fast as it dissolves it in the sap it generally changes it into 

 sugar. Mucilage, starch, sugar, and plant-fabric, all have the same chemical com- 

 position, or very nearly ; and the plant readily changes one into the other as it needs. 

 Notice the changes of vegetable matter in a plant of Indian Corn. In the leaves, 

 where it is made, the elaborated sap is in the form of mucilage ; in the stalk, at 

 flowering-time, while on its way to form and nourish the blossoms and grains, it 

 turns sweet, being changed into sugar ; in the grain, a part is changed into starch 

 and laid up there : when the grain germinates, the starch is dissolved and changed 

 back into sugar ; and in the growing plantlet which it nourishes, the sugar is at 

 length changed into plant-fabric. 



273. Circulation or Conveyance of Elaborated Sap, or Dissolved Vegetable Matter. The 



new-made vegetable matter rarely accumulates in the leaves where it is made, ex- 

 cept in the Century-plant, Houseleek (Fig. 6-5), and other fleshy-leaved plants. 

 It is generally distributed through all the plant (that is, thi'ough all its living parts), 

 or carried especially to where a stock is to be laid up, or where growth is taking 

 place. So the elaborated sap, passing out of the leaves, is received into the inner 

 bark, at least in trees and shrubs,- — or in herbs it may descend through the soft 

 parts generally,- — and a part of what descends finds its way even to the ends 

 of the roots, and is all along diffused laterally into the stem, where it meets 

 and mingles with the ascending crude sap or raw material. So there is no separate 



