BOTAN1T. 107 



numerous branches near the ground, and do not attain the 

 size of trees : such are the alder, whortlebeny, lilac and haw- 

 thorn. 



Trees have perennial, woody stems and roots, do not 

 branch off near the ground, and attain a great size : examples, 

 elm, oak and pine. The distinguishing property of the stem 

 is the production and development of luds. 



Buds are of two kinds, viz: the leaf -bud and the flower-bud. 



The leaf-bud consists of delicate layers of cellular tissue, or 

 embryo leaves, covered by hardened crusty scales. 



The "flower-bud consists of the rudiments of the new flower. 



There are several subordinate organs, which are little more 

 than appendages to the stem, and which it is unnecessary to 

 describe. 



STRUCTURE AND FUNCTIONS OF THE STEM. 



Plants are divided into exogenous and endogenous. 

 The exogenous are those which grow by accumulation, or 

 layers of matter from the outside. This class includes nearly 

 all forest trees and most shrubs and herbaceous plants of tem- 

 perate climates. 



The endogenous plants are those which grow from the inside, 

 or by accretion of matter within that already developed. Most 

 of the bulbous plants of temperate regions, all the grasses, and 

 the palms, cane, <fec., of tropical countries, are endogenous. 

 The exogenous stem consists of bark, wood and pitL 

 The pith is a light spongy substance, at the centre of the 

 stem : it is composed of cellular tissue, and seems to exercise 

 its peculiar functions only during the earlier growth of plants. 



[Wood. 



The icood is composed of cylindrical or concentric layers, in- 

 tersected by medullary rays, which are those thin dense plates 

 of wood dividing the "grains," and are large and easily seen 

 in a piece of beech or oak wood which has been split. The 

 pith, together with the first layer which incloses it, are the 



