42 



HOW PLANTS GROW. 











of the whole. Such stems may Avell enough be called inside-groivers, because their 

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

 libres of wood within or amons; the old. 



114. Moreover, endogenous stems 

 are apt to make few or no brandi- 

 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 hke, 

 seldom branch until they come to 

 flower ; and Palms are trees of 

 tliis 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. Tlic Exogenous Stem is the 



kind we are familiar with in ordi- 

 nary wood. But it may be observed 

 in tlie 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 Avoody 

 bundles soon appearing to 

 run toirether into a solid 

 layer. This layer of wood, 

 whether much or little, is always situated around a central part, or p^V/^, 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 



PaliucUus of vuriuUa a^ea, and a Yucca, y. 



