﻿MR 



HN SCOTT ON THE TREE FERNS OF BRITISH SIKKIM. 15 



a similar increase lateraUy is, I belieye, due to the flabeUate venation, which radially 

 concentrating the organizing force in the frond, thus demarcates and limits the growth 

 of the stipe m a much more decided manner than is the case in fronds with lateraUy 

 developed segments, in which the stipe blends into the rachis *. 



I may in this place cursorily refer to the opinion that the trunks of tree ferns are 

 hollow when fully formed, as stated in most of our botanical class-books. I can scarcely 

 think that this is founded on observations of living or at all fresh specimens, but 

 that It rather has an origin in the examination of dry museum specimens, which are then 

 of course hollow. I at least have seen no such appearances in the many tree ferns 

 I have seen growing in their native habitats. On the contrary, I have found, as shown 

 m Plate L, representing the basal portion of a trunk of Alsox>Ula laiehrosa 7 feet hi-h 

 that there is a greater tendency to consolidation by the descent of woody bundles from 

 the fronds than to any rupturing or hollowing of the internal parts, throughout which at 

 least a passive vitality is long continued. There is this, however, to be said, that species 

 vary much m the tendency to throw out adventitious roots {e, g. Hendtella decipiens has 

 those roots confined chiefly to the base of the stem, while under the same conditions in 



* A cognate and, in my opinion, very excellent illustration of the influence of mechanical actions on the formation 

 of wood 18 presented by those hnge buttresses which we find so common in many of the timber- and other trees of 

 India. Probably the Paddlewood of Guiana {Aspidosjiermum ea^cehum), the Logwood {Ecematowyhn cam^ecManum) 

 &e. have a like origin; and I do not doubt that the degree of fluting will be found to vary in individuals with their 

 mechanical and physical conditions. But that this is the case with Logwood I have evidence from the plants in the 



Calcutta Botanic Gardens. 



Tectonci 



deteriorated by this buttressing process, which seems to me not a specific, but rather a local characteristic. In the 

 Botanic Garden here the buttresses are generaUy large in proportion to the diameter of the trees ; and we find the 



„„„„ j„,, 1 . . . , ^^y^ ^^^ distributed in a horizontal manner near the surface— a result, no doubt 



alluvial 



dr 



vigour, indicating that, for the production of first-class 



Even in those conditions, however. Teak springs up with a wonderful rapidity and 



of their roots, reduce the size of the buttresses, and render them less liable to be uprooted in the storms which of late 



these parts. The buttresses are thus, in my opinion, simply an efibrt of nature to com- 



Visited 



surface 



boles. The accordance of this with 



with deeply penetrating roots comparatively free from buttresses and with plane unfluted 



when we consider the respective mechanical 



conditions. Thus in those with roots more or less acutely penetrating the soiL there will 

 ot the axis of resistance in lines concentric with the main axis of the tree, and a consequently graduated equality 

 in the develpment of the woody layers as afforded by the plane and rounded boles. Again, in those with roots 

 diverging at obtuse angles, there must' necessarily be an isolation in the strains or resisting axes, each root forming 



• 



will 



matter in axes continuous with those of the roots, decreasing upwards with the convergence of these axes. This 

 accords with the nhenomPTinTi iti ^t^^^o4^^^r^ v^,,+4-*.^«««^ a^ j -i^ i 1 1 * . 



surface 



I have also observed that trees with branches diverging at more or less acute angles from the main ^ 



trunk are generaUy more strongly buttressed than those with 

 explanation of wl 



1 1 



former 



further illustrating this mechanical theory 



buttresses of a tree are rarely (I beUeve, never) directly opposite, as might have been expected had 



H 



nutrition 



; furthermore, in the Botanic Gardens here— I have not particularly noted 

 his point elsewhere-the largest buttresses are, or rather were (for the cyclones have left us few to look 

 t) on the side of the prevailing winds. 



