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MR. JOHN SCOTT ON THE TREE FERNS OF BRITISH SIKKIM. 



25 



characterized, and the consequent compression of the surrounding cellular tissue 

 render it denser and harder, so that the lower parts are always much harder and 

 more woody than the upper. Mechanical strains are also potent agents in the increase 

 of the dense deposits ; and we have further, in the general distribution of the woody 

 system, a peripheral woody casing surrounding a cellular core, the simplest though not 

 the least effective mode of resisting such tensions 



8. In transverse sections the woody framework appears in from three to five detached 

 peripheral laminae, the difference in number being due to variations in the frond-arran ce- 

 ment of the different species. The interspaces indicate the position of the fronds and 

 vary m width, according as they are more or less near the axis of the latter, as explained 

 by their lozenge-shaped appearance in the longitudinal sections. In fresh sections the 

 woody lamm^ usually present concavo-convex surfaces, less commonly irregular wavy 



outlines 



sections of dried specimens, On the other hand, the laminse present 



curvatures, according to the less or more regular drying of the stem. In this process the 

 laminae are frequently broken; so that there are frequently more of them than normallv 

 characterize the species. 



9. The transverse sections of the apex of' the stem have a somewhat complex arrano-c- 

 ment, representing the nascent woody system, and indicating the points of orio.in^)f 

 several successive cycles of fronds. The points of origin of the fronds are thus organically 

 predetermmed by the vascular system ; and their distribution can have nothing whatever 

 to do with the distribution of this, and of course infinitely less in its compaction 

 The idea of the caudex as a product of the coalescent bases of the fronds is 



unfounded 



wholly 



10 The caudex of ferns retains its solidity to tlie last, and has, as above explained 

 a tendency to increase in density and hardness. It is a mistaken notion of authors to' 

 represent the stem as frequently hollow at the base by the rupture of the central cellular 

 axis This view could only have been founded on the examination of dried caudices in 

 which, as a matter of course, we find the ceUular parts irregularly ruptured or, indeed 

 wholly absent. Such results do not occur in the living plant, or at least could there only 

 be the result of physical injury or the destructive inroads of the boring beetles 



11. The distribution of the vascular system in the caudices of the" dwarf herbaceous 

 ^ecies diifers only in the degree of development from that of the arborescent species 

 l^ongitudiual sections exhibit no continuous strata; all are short and detached and 

 wanting m the regularity of distribution of the arborescent kinds, though the general 

 woody filaments, as in young individuals of the latter, foi-m a peripherical network with 

 more or less regular lozenge-shaped meshes. The fibro-vaseular bundles of the fronds 

 are given off along the sides of the meshes, and pass into the stipes in a laminar form 

 m this respect differing from the arborescent species, as also in the entire absence of the 

 free woody bundles. In those species where one bundle only passes into the stipe it is 

 given off at the upper angle of the mesh. The distribution of the fibre vascular system 

 is very clearly shown to be in no way causally effected by the disposition of tlie fronds l,v 

 an examination of the tubers of Nephrolepis tuberosa, in which we find radiatiu- from 

 the solitary vascular bundles of the stolon a number of thin wii-y fibres variously aMsto 



VOL. XXX. 



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