ENDOGEN 



and the thrusting of the leaves to which they belong from the centre t.> the 

 circumference. Such a case throws great light upon the real nature of the 

 more regular forms of endogenous « 1. 



Other appearances are owing to imperfect development, as in - 

 the aquatic Bpecies of this class. Lemna, for example, has itc and 



leav( 1 together into a small lenticular cavernous body; and in Zanni- 



chellia and others, a few tubes of lengthened cellular tissue e.m.-titute aln 

 all the axis. 



By far the most striking kind of anomaly in the stem of Endogens is that 

 which neeurs in Barbacenia, ami which was originally noticed in the first 

 edition of this work, p. 334. In an unpublished species of Barbacenia from 

 Rio Janeiro, allied to P>. purpurea, the Btems appear externally like tl. 

 of any other rough-barked plant, only that their surface is unusually fibn 

 and ragged when old, and closely coated by the remain.- of sheathing leai 

 when young. Upon examining a transverse section of this - m it is found 

 to consist of a small firm pale central circle havingthe ordinary endogen- 

 ous organisation, and of a large number of smaller and very irregular oval 

 spates pressed closely together but having no organic connection ; between 

 these are traces of a chatfv ragged tissue which seems as if princi- 

 pally absorbed and destroyed. A vertical section of the thickest part ol 

 thi> stem exhibits, in addition to a pale central endogenous column, woody 

 bundles crossing each other or lying parallel, after the manner of the 

 ordinary ligneous tissue of a palm stem, only the bundles do not adl 

 each ether, and are not embodied as usual in a cellular substance. Th 

 bundles may be readily traced to the central column, particularly in the 

 younger branches, and are plainly the roots of the stem, of exactly the 

 same nature as those aerial roots which serve to stay the stem of a sen 

 pine (Pandanus). When they reach the earth the woody bundles become 

 more apparently roots, dividing at their points into fine nts, and 



entirelj resembling on a small scale the roots of a palm-tree. The central 

 column is much smaller at the base of the stein than near the up] 

 extremity. A figure of this structure will be found under the ord 

 Hsemodoracese. 



The aire of endogenous tree- has been little studied. When the circum- 

 ference of their stem is limited specifically, it is obvious that their hves will 

 be limited also; and hence we find the longevity of palms inconsiderable 

 when compared with that of exogenous trees. Two or three hundred 3 

 are estimated to form the extreme extent of life in a date palm and in many 

 others. But where, as in the Dragon Trees, the degree to which th< - 

 will grow in diameter is indefinite, the age seems, as in I -. to be 



indefinite also: thus a famous specimen of tin- Dracssna Drai 0, 

 in Teneriffe, was an object of great antiquity so long ■•.. D. 141 



and is still alive. 



Important as the character furnished by the internal inann. owtl 



of an Endogen obviously is, it is much enhanced in value 1 ••, found 



very generally accompanied by peculiarities of organisation 111 otnei 

 The leaves have in almost all cases the veins placed in parallel lii 

 connected by transverse single or nearly Bingle bars. Straight 

 foliage is therefore an external symptom of an endogenous mod. th. 



When su.-h an appearance is found in E: il is always fallacious, and 



is found to be owing to the excessive size and peculiar direction 

 the larger veins, and not to be a general character of all the 1 m ; 



as is sufficiently obvious in Rib-gr ntian, and many more. 



