ENDOGENS. 99 



and the thrusting of the leaves to which they belong from the centre to the 

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

 more regular forms of endogenous wood. 



Other appearances are owing to imperfect development, as in some of 

 the aquatic species of this class. Lenina, for example, has its stem and 

 leaves fused together into a small lenticular cavernous body ; and in Zanni- 

 cheliia and others, a few tubes of lengthened cellular tissue constitute almost 

 all the axis. 



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

 which occurs in Barbacenia, and which was originally noticed in the first 

 edition of tliis work, p. 334. In an unpubhshed species of Barbacenia from 

 Rio Janeiro, alhed to B. purpurea, the stems appear externally like those 

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

 and ragged when old, and closely coated by the remains of sheathing leaves 

 when yoimg. Upon examining a transverse section of this stem it is found 

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

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

 spaces pressed closely together but ha\'ing no organic connection ; between 

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

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

 this 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 adhere to 

 each other, and are not embodied as usual in a cellular substance. These 

 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 screw 

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

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

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

 column is much smaller at the base of the stem than near the upper 

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

 Haemodoracese. 



The age of endogenous trees has been little studied. When the circum- 

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

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

 w^hen compared with that of exogenous trees. Two or three hundred years 

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

 others. But where, as in the Drao-on Trees, the deo-ree to which the stem 

 will grow in diameter is indefinite, the age seems, as in Exogens, to be 

 indefinite also : thus a famous specimen of the Dracaena Draco, of Oratava 

 in Teneriffe, was an object of great antiquity so long ago as a. d. 1402, 

 and is still alive. 



Important as the character furnished by the internal manner of growth 

 of an Endogen ob^^ously is, it is much enhanced in value by its being found 

 very generally accompanied by peculiarities of organisation in other parts. 

 The leaves have in almost all cases the veins placed in parallel lines, merely 

 connected by transverse single or nearly single bars. Straight-veined 

 foliage is therefore an external symptom of an endogenous mode of growth. 

 When such an appearance is found in Exogens it is always fallacious, and 

 is found to be owing to the excessive size and peculiar direction of a few of 

 the larger veins, and not to be a general character of all the venous system ; 

 as is sufficiently obvious in Rib-grass, Gentian, and many more. 



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