38 ELEMENTARY ORGKANS OF PLANTS. 



are probably only a modification of one universal principle of 

 vital action. 



40. In Forest-trees, the process of growth, or cell-evolution, 

 continues for centuries; in shrubs, for a much shorter space 

 of time : hence, the vast size to which the former attain, and 

 the dwarfed growth of the latter. In these plants, the cells, 

 as they increase in number, become specialized, or arrange 

 themselves into definite parts, such as root, stem, and leaves, 

 each having distinct functions to perform in the vegetable 

 economy, whilst their reproductive cells are contained in 

 certain metamorphosed and terminal leaves termed anthers, 

 and are the final results of the physiological action of an 

 exquisite floral apparatus bright with the most resplendent 

 hues and colors. Eorest-trees and shrubs are the highest 

 forms of vegetable development on the face of the earth. 

 Not only do they surpass the herbaceous plants, that grow 

 beneath their shade, in size and in the duration of their life, 

 but they are to a considerable extent more composite in their 

 mode of growth. The forest-tree is not a simple individual, 

 as is usually supposed, but a community of individuals. 

 Properly speaking, the simple plant consists only of a stem, 

 root, and the first pair of leaves. The succeeding evolution 

 of leaves is only a continuation of the first process of growth, 

 whUst each bud is an actual repetition of the plant, the only 

 difference being that the bud or new plant has no free radical 

 extremity, like the parent plant, developed on the soil, its 

 root being intimately blended with and contributing to the 

 formation of the wood of the stem on which it grows. 



41. In Shrubs and herbaceous annuals and perennials, there 



