﻿MR. JOHN SCOTT ON THE TREE FERNS OF BRITISH SIKKIM. . 13 



which seem in the transverse sections to have an isolated position, have not really such, 

 as will be seen by a reference to the longitudinal section of A, glabra (PL V. fig. 2), in 

 which the woody laminae are continued upwards and along the flattened apex. At this 

 period of development the structure scarcely differs from that of a young Dicotyledonous 

 stem, with which type they further agree in undergoing a certain degree of lateral 

 development, until all unite and form a simple tabular circle with spirally arranged 



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lozenge-shaped openings, enclosing a central parenchymatous mass, and enveloped in a 

 cellular rind. There, however, the analogy ceases ; and the vital activity, no longer 

 directed to the lateral development in the periodical addition of layers (as in Dicotyledons) 

 to these closed portions, is continued upwards in newer cycles. A lateral and a front 



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view of the woody framework of A. latebrosa, prepared by maceration, is shown on 

 PL III. ; and I have also given, by way of comparison, sections from the stem of 

 Asplenium esculentum (PL XII.). The latter presents a more or less regular series of 

 lozenge-shaped meshes, from the lateral angles of which two vascular bundles pass oif 

 into the fronds. In the stems of tree ferns the woody framework is much more largely 

 developed, and a numerous series of branches proceeds from the whole margin of the 

 ellipsoidal spaces for the supply of the fronds, and is not limited, as in the herbaceous 

 species, to the anastomoses of the main bundles. It will also be observed, by a reference 

 to PL III. fig. 4, that these lateral or frond-bundles pass off from the main framework 

 in an isolated-cylindrical state, rarely dividing again as they penetrate the diaphragm of 

 the frond. 



The arrangement of the woody tissue in the stems of the dwarf herbaceous species is, 

 as might be expected, much less regular than in those of the arborescent species. The 

 irregular distribution of the former is well shown in the various sections of Asjplenium 

 esculentum represented in PL XII. These differences in the distribution of the woody 

 tissue in the dwarf and arborescent species are no doubt due to the inverse relations, 

 pointed out by Spenser, between the formation of woody tissue and the subjection to 

 mechanical strain. This seems to me borne out by the fact that individuals of the 

 same species when frequenting different habitats — for example, the Asplenium esculentum 

 above referred to, which indifferently occurs on dry banks and old walls, or under the 

 deepest shade (in ditches and by the sides of tanks) — ^present considerable differences 

 in the degree of development of the woody tissue, those presenting the greatest amount 

 of the latter being invariably the individuals from the deepest and most sheltered 

 habitats. In the arborescent species we also find considerable differences : in the 

 individuals from dense forest clad ravines the woody laminae are decidedly thinner 

 and interposed with thicker layers of parenchyma, the arrangement of the fronds 

 becomes less regular, and the interspaces are freciuently greatly increased. The. sections 

 of A. contaminans, represented on Pis. IV. & IX., show this in a very marked manner. 

 The latter of these, with the distantly arranged fronds, oblong scars, with ii-regularly 

 distributed inner vascular bundles, is drawn from a living specimen in the fernery of the 

 Botanic Gardens, Calcutta, and presents a striking contrast to the symmetrically 

 arranged quadrate scars and arcuately distributed vascular bundles which were afforded 



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by the other section of a specimen which I cut on the Poomong Cinchona- lands (PL IV. 



