DEVELOPEMENT OF VEGETABLES. 83 



conducting their growth.* In the greater num^ 

 ber, the successive additions to the substance 

 of the stem are made on the exterior side of the 

 parts from which they proceed. This mode is 

 adopted in what are called Exogenous plants. In 

 others, the growth is the result of additions made 

 internally ; a plan which is followed in all En- 

 dogenous plants. The Oak, the Elm, the Beech, 

 the Pine, and all the trees of these northern 

 regions, belong to the first of these divisions. 

 The Palm tribe, such as the Date, the Cocoa-nut 

 tree, and, indeed, a large proportion of the trees 

 of tropical climates, together with the sugar- 

 cane, the bamboo, and all gramineous and lilia- 

 ceous plants, belong to the latter. We shall first 

 inquire into the endogenous mode of growth, 

 as being the simplest of these two kinds of vege- 

 table developement. 



A Palm tree may be taken as an example of 

 the mode of growth in endogenous plants. The 

 stem of this tree is usually perfectly cylindrical, 

 attains a great height, and bears on its summit a 

 tuft of leaves. It is composed of an extremely 

 dense external cylindric layer of wood ; but 

 the texture of the interior becomes gradually 



* The tribe of Filices, or ferns, the structure of whicli is 

 vascular, constitute an exception to this rule : as they differ in 

 their mode of developement, both from exogenous and endoge- 

 nous plants. 



