42 



llUW PLANTS (iUOW. 



:| l!l 



now thrciuls or fil)re.s of wood wiUiiii or amon^' the old. 



ment of tho wliol»\ Riich stems may well (moii^jh be eallecl insiflf-f/rowfii'Sy 

 because their wood ineieases in amount, as tht-y <,'i-ovv oldei-, by the formation 

 of 



114. Moreover, ondo<,'enous stems 

 are apt to make few or no branches. 

 Asparagus is tho only common 

 examj)lo to tho contrary; that 

 branduis freely, lint the stalks of 

 Corn Jind other grain, and those ,.-<^;;j;a^ 

 of Lilies (Fig. i, 2) and tlio like, 



seldom branch until they come tf) ^r'^-i 

 flower ; and Palms are trees of this "(Z^^'M^ 

 sort, with perfectly simple or branch- 

 less trunks, rising like columns, and 

 crowned with a tuft of conspicuous 

 and peculiar foliage, which all comes 

 from the continued giowth of a ter- 

 minal bud. 



115. The Exogenous Stem is tho 



kind we are familiar with in ordi- 

 nary wood. But it niav be observed 

 in tho greater part of our herbs as 

 well. It dilVers from the 

 other cla.ss, even at tho 

 beginning, by the wood all 

 oi3Cupying a cej'tain part of 

 the stem, and l)y its woody 

 bundles soon appearing to 

 run together into a solid 

 layer. This layer of wood, 

 W'hether much or little, is always situated around a central part, or }^ith, which 

 has no wood in it, being pui-e c< llular tissue, and is itself surrounded by a bark 

 which is mainly or at tirst entirely cellular tissue. So that a slice across an 

 exogenous stem always has a separate cellular part, as bark, on the circumfer- 

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



1/ 7!» 



Palmi'ttos of various ngos, and a Viicca, j/. 



