﻿MR. JOHN SCOTT ON THE TREE FERNS OF BRITISH SIKKIM. 9 



Inferred to above (tab xxix.fig. 2), gives a section of the stem oiAlsopMla e.celea of ar 

 actangu ar outline, winch I have never seen any fern assume. This section presents 

 n^eworthy pecuhanty a so in the peripheral line of large isolated vascular' bunis 

 which occur m none of the specimens that have come under my observation. I suspect 

 however, that though in no way distinguished by Mohl from normal woody bundles' 

 they are merely isolated masses of parenchyma, such as we often find dried sections pre' 

 sentmg, and, mdeed, partially illustrated in the section of SemiieUa dcoipiem (PI I 

 fig. 4). This receives a further confirmation by reference to the magnified portions of the 

 above sec ion (Mohl, tab. xxxii. figs. 1 & 2), wliich present no vascular tissue in 



iponding stratum 



the 



of 



The soft central mass consists of parenchyma, intersperied (as in PL I. fig. 2) more or 

 less wi h, or nearly destitute of, isolated vascular bundles. These bundles present 

 externally a layer of hard brown pleurenchyma, succeeded by a layer of soft paren- 

 chyma which surrounds a trachenchymatous axis. With regard to the development of 

 these bundles, the generally received opinion (in unison with the theoretical distinction 

 of acrogens) IS, that they grow from below upwards, and never in any case extend below 

 the pomt at which they originated. This opinion, however, by no means agrees with 

 my observations, throughout which I have invariably found that they originate partlv 

 trom the axial tissues in proximity to the hard brown diaphragm of the frond and 

 partly from the margins of the meshes in the woody laminw at the point of origin of the 

 latter This is very clearly demonstrable by examination of the nascent fronds „. 

 AUopktla ornala and lateh-osa. The transverse section of the apex of a caudex of 

 A latebrosa (PI. III. fig. 3) shows the structure and arrangement of the young fronds 

 Now, in examining these, we find as we pass from those on the periphery to those in the 

 centre the number of free vascular bundles decreasing, and wholly disappearing in the 

 younger or nascent fronds-a result, of course, equally accordant with either view^of then: 

 origm. Longitudinal sections, however, afford us conclusive evidence, showin- the 

 vascular bundles in various stages of development (and, as they appeared to me. aJways 

 younger and less perfect towards their respective extremities) in the young frond and 

 parenchymatous axis. In their centre, or line of separation of the frond and the caudex 

 they consist of parallel lines of trachenchymatous tissue, surrounded by thin elon-ated 

 cells, which pass by a gradual transition into the ordinary parenchvmatous tissue of the 

 stem, as m their upward growth they pass by a similar transition into the cellular tissue 



of the rachis 



As supporting the view I have taken, I may further remark on the 

 absence of the bundles from the apical part of the stem, and the non-appearance of 



i)arati\ 



such 



pward course of development. In all cases in wliich I have heen able 

 to trace them to their extremities, I have invariably found a developing apex below 

 and a more perfectly developed tissue upwards, .passing into a stipe. Eurthermore, I 



mstance observed upwardly-developing ramifications from lower bundles 

 which evidently should have occurred had the theory of development from below been 

 correct, whereas aU seem to me confirmatory of the opposite view, and point to the 

 inosculations of descending bundles. In A. latehrosa the free vascular bundles are 



have 



VOL. XXX. 



c 



