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JOHN SCOTT ON THE TREE FERNS OF BRITISH SIKKIM. 31 



not be difficult to prove that all the modifications of woody tissue in ferns occur in every 

 essential point in the Cactacese and the succulent Euphorbiace^." With reference to 

 this I have to remark that the arrangement of the vascular bundles in the first stages 

 differs but little from, that characteristic of the young shoots of dicotyledonous plants in 

 general, and that ultimately they seem to me to find their closest relationship, struc 

 turally and physiologically, in Cycads, more remotely with Nymphjeas. They (the 

 Cacti) have thus but a very indirect connexion with the Perns ; and I should not have 

 noticed them here but for Schleiden's remarks, from which I may assign the following 

 reasons for differing : 



In Cacti, the composition of the stem is :— 1st, a central parenchymatous mass ; 2nd, 

 a zone of vascular bundles separated concentrically, and also in a partial manner radially^ 

 by thin cellular layers ; and, 3rd, a largely developed cortical parenchyma. In Cycads 

 the general arrangement is much the same, the difference being more in degree than 

 kind ; thus, the concentric zones have thicker layers of cellular matter interposed, and 

 the intrusion of the cortical parenchyma in vertical planes is very much more marked, 

 giving to. the wood a peculiar tendency to split up, when dry, into thin radial laminae! 

 Such, then, are a few of the more prominent structural relations of Cycads and Cacti, 

 to which I may add the following physiological ones. It is well known that Cacti are 

 singularly tenacious of life ; but it is not so generally known that Cycads possess 

 the same quality in an equally high degree. An uprooted Cycas, even in ordinary 

 forest shade, will produce adventitious roots and an abundance of adventitious buds 

 from all parts of its stem ; so also with Cacti, though with much less facility when the 

 stem is otherwise uninjured. Again, when the stems of a Cycas are broken o&, the 

 surface is readUy closed over by a development of the cortical and intravascular 

 parenchyma, whence adventitious buds sooner or later proceed. In Cacti the intra- 

 vascular parenchyma is less active than the cortical ; and we find that under similar 

 conditions to those noted in Ci/cas a thick surrounding " caUus " is developed from 

 the cortex, while a few cellular papiUse, " embryo buds," are the products of the 

 intravascular cellular layers. In all the above characters therefore there is a 

 siderable similarity between Ci/cas and Cacti. There is thus evidently a wide gap 

 between the anatomy of the stems of Cacti and tree ferns, between which, if I mistake 

 not, ISTymphseas may be very naturally interposed, as combining a living type of exogenous 

 flower structure with an acrogenous development of the stem. 



With regard to habit and arrangement of the reproductive organs, the tree ferns, 

 as has been frequently remarked, have considerable affinity to Cycads ; but from my 

 observations their further relationship by a circinate vernation is unfounded. I have 

 been particularly observant on this point, and write from repeated examination of 

 plants in their own habitats as well as those in the Eotanic Gardens, Calcutta ; and in no 

 case have I seen cii-cinate fronds on a Cycad. While I now write I have before me the 

 young unfolding fronds of the foUowing species :— Cym^ circinalis, Linn., C. Bumphii, 

 Miq., C. revolula, Thunb., C. siamensis, Miq., aU of which have a straight vernation, 

 with involute pinnae ; and this, I suspect, has been the origin of the opposite view now 

 80 generally adopted by authors, apparently on the authority of Linn^us and Uoxburgh's 



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