38 TALKS AFIELD. 



from the manner in which these inside grow- 

 ers increase in diameter that there must soon 

 be a limit to this increase. In tree-like 

 plants the outside or bark portion soon be- 

 comes so indurated as to resist further 

 stretching, and even if this were not the case 

 it is scarcely conceivable that new fibres could 

 long be added in the interior. Endogenous 

 plants seldom become large in diameter. 

 Most palms are as thick when they begin to 

 ascend from the ground as they ever will be. 

 As a rule palms do not branch ; they grow 

 entirely from the terminal bud, and if this 

 bud be destroyed the plant perishes. Endo- 

 gens have no true bark, none that can be 

 readily stripped off, and they have no pith. 

 The grasses, sedges, the lily tribe, the or- 

 chids, and the rushes are endogenous plants. 

 Exogens include our woody plants and our 

 trees, and also many of our herbs. If we 

 strip the bark from any of our trees in 

 spring we shall find a mucilaginous covering 

 remaining on the wood. This covering is 

 being made for the formation of new wood. 

 It is cellular in character ; the walls of its 

 minute cells are thin, and the cells themselves 

 contain building materials in the liquid state. 

 This new layer is the cambium ; upon one side 



