42 



HOW PLANTS GROW. 



of the whole. Such stems may well enough be called inside-growers, because their 

 wood increases in amount, as they grow older, by the formation of new threads or 

 fibres of wood within or among the old. 



114. Moreover, endogenous stems 

 are apt to make few or no branch- 

 es. Asparagus is the only common 

 example to the contrary ; that 

 branches freely. But the stalks 

 of Corn and other grain, and those 

 of Lilies (Fig. 1, 2) and the like, 

 seldom branch until they come to 

 flower ; and Palms are trees of 

 this sort, with perfectly simple or 

 branchless trunks, rising like col- 

 umns, and crowned with a tuft of 

 conspicuous and peculiar foliage, 

 which all comes from the continued 

 growth of a terminal bud. 



115. The Exogenous Stem is the 



kind we are familiar with in ordi- 

 nary wood. But it may be observed 

 in the greater part of our herbs as 

 well. It differs from the 

 other class, even at the be- 

 ginning, by the wood all 

 occupying a certain part of 

 the stem, and by its woody 

 bundles soon appearing to 

 run together into a solid 

 layer. This layer of wood, 



whether much or little, is always situated around a central part, or pith, which 

 has no wood in it, being pure cellular tissue, and is itself surrounded by a bark 

 which is mainly or at first entirely cellular tissue. So that a slice across an exoge- 

 nous stem always has a separate cellular part, as bark, on the circumference, then a 

 ring of wood, and in the centre a pith ; as is seen in Fig. 80, representing a piece 



!/ '79 



Paimetlus of variuus ages 



