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SCOTT ON THE TREE FERNS OF BRITISH SIKKIM. 23 



the flowers than any merely protective agency ; anyhow this is highly probable from the 

 relations so^ well explained by Herbert Spencer {vide ' Principles of Eiology,' chap. x. 

 p. 146, vol. ii.). It is there shown that aU radially symmetrical floWers have vertical 

 axes, and that deviations from this symmetry are in aU probability adjustments to the 

 fertilizing process. Mr. Herbert, adopting Darwin's views, reasons thus :— « So long as 

 the axis of a flower is vertical and the conditions similar all round, a bee or butterfly 

 alighting In it will be as likely to come from one side as from another ; and hence 

 hindrance rather than facilitation would result if the several sides of the flower did not 

 afford it equally free access. In Hke manner, flowers which are distributed over a plant 

 m such ways that their disks open out on planes of all directions and inclinations wiU 



have no tendency to lose their radial symmetry but flowers so fixed as to open 



out sideways in tolerably constant altitudes have their petals differently related to insect- 

 agency ..... A long undermost petal or Hp, by enabling the insect to settle in such 

 a way as to bring its head opposite to the opening of the tube, aids its fertilizin 



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agency ( p. 153). Now, in the cases of circination referred to (for example, in Myosotis), 

 we find first radial symmetry of the flowers with a second arrangement, so that as the 

 stem unfolds the flower passes from the inverted to the upward position of the mouth 



and ultimately, and probably after the fertilization, assumes a lateral position on the 

 axis. ^ Thus, as I believe, circination, though subserving (as in the above cases) distinct 

 ends in the plant's economy, has been acquired through " natural selection," which, 

 "working" (as Mr. Darwin weU expresses it in reference to somewhat cognate cases i 

 vide * Origin of Species,' 3d ed. p. 213) « for the good of each being, and taking advantage 

 of analogous variations, has sometimes modified in very nearly the same manner two 

 parts in two organic beings, which beings owe but little of their structure in common 

 to inheritance from the same ancestor." 



I will now briefly summarize the peculiarities and affinities of tree ferns, commencing 

 with the development of the embryo plant. 



1. The first product of the spore is the prothallium, with its antheridial and arche- 

 gonial cells, which by a fertilizing process give origin to an embryonic body, whence 

 proceed the fronds and caudex. 



2. In the earliest stages of the caudex transverse sections exhibit only one vascular 

 bundle. The point of origin of this in the stem is predetermined by the first frond, 

 whence the longitudinal axis of the nascent fibro-vascular bundle is directed. This 

 fibro-vascular bundle grows upwards and outwards into the first frond, with which it is 

 subsequently simultaneously developed ; again, from the lower end of the bundle _ 

 branchlet passes out into the first root. With the development of the primary frond 

 and root there is a simultaneous and somewhat rapid apical growth of the young stem, 

 and a continuation of the primary vascular bundle to the point of origin of the second 

 frond. A similar development of the stem and vascular bundle is continued until the 

 appearance of the sixth or even the ninth frond. In all the Sikkim species of which 

 I have had an opportunity to examine young plants, the frond-arrangement is thus far 

 tristichous, and the angular divergence, of course, one third. The stem is now veiy per- 

 ceptibly increasing in thickness, and depressed or flattened at the apex; the angular 



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