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



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mosing, and forming a polygonal network concentric with tlic cellular knob. Again, in 

 no respect do the elongated frondless ends of the shoots of such sj>ccics as Acrostichum 

 {Stenosemia) scandens, Folypodium {I*hego])terls) j^unctatwm^ and other widolj creep- 

 ing species, differ from the frond-hearing parts. 



12. Adventitious roots originate indifferently on the cortical region and the interior 

 woody laminae. Those originating in the former region are most abundantly produced 

 in certain species (Alsophila latehrosa and A. coutaminans) ^ and give quite a shagreen- 

 like covering to the stem in their younger stages. It is only in the moistest forest 



n 



tracts where these undergo any considerable degree of development ; and that stroi 

 thick matting which so frequently surrounds the caudex (exceeding by many times the 

 diameter of the latter) is chiefly composed of those roots which spring from the interior 

 laminae. The points of origin of the adventitious roots are by no means fixed, appearing 

 in all the interfrondal spaces of the caudex. In no case, however, are thev continua- 

 tions of the free woody bundles, nor do they partake of their anastomosini? character, 



though greatly exceeding them in their tendency to ramify 



D 



. The diaphragm or " separating layer," between the proximal and distal parts 

 of the frond, occurring (as I stated above) m both deciduous and nondeciduous 

 species, can scarcely, in my opinion, be regarded as a truly causal agent in the phe- 

 nomena of defoHation. Von Mohl and Eichler, who have studied the subject, and 

 were the first to detect the « separating layer," afford but slight grounds for the suppo- 

 sition of its causal relations to the faU of the leaf; nor do they afford us any sort of 

 explanation as to how this secondary growth may have been initiated. With regard to 

 the first point, while admitting certain incidantal relations which might haye justified 

 the adoption of the views of Von Mohl in the absence of any positive evidence of a 

 negative character, we have the occurrence of the « separating layer " somewhat indif- 

 ferently in deciduous and non-deciduous species, as, for example, in the tree ferns noted 



above: 



must take 



then there is the regulated specific periodicity of the fall of the leaf, which 



into consideration as probably related to those physico-vital processes less or 



more active m all vegetable development. The fall of the leaf occurs, as we aU know, at 

 :t'':y ^:":^^ ^^!'Z^''^ .'^'^'^''^ - -^-'l-^. j-t as m aoral periodicity, 



more 



faruTble t J r^'^'^''^' rf^'^^ - - -"elation of conditions less or n.ore 



Kes^ol in the t ''T °' *^'" ^"^'^"'*°"- " '''^ "^ ^'^^^ t'^^t deciduous 

 trees grown m the tropics become evergreen-the Cherry for example. Of this I know 



nothmg from personal observation ; hut if like the Vine, the Pear, and the Tp e wS 



periods of Vernation and def o"^th Lif d^^e ^^e tf aTi^f ^ '''''' 

 susUined by the continued evolution of young shootsTnT W^ T^tSj^Z'Z 



shed with considerable regularity twice a vpnr fircf «+ +i. i .. ./ 



the ushering in of the hot, 'and agL be wee^ L tt^^^^^^^^^^^^^ t *'^? ^^^ f r '"' 



~ment of the cold season. In view of the fo^oTg evidLct TZ tT . ""d" 

 to heheve that we must yet continue to regard these Vno^enT:' tleTesulTo^r; 



i 



