Dr. G. Ogilvie on the Forms and Structure of Fern-stemsi 409 



central axis of the rootlet, and force their way outwards through 

 the tissue of the cortical zone in which they were developed. 

 Without venturing to say how far this local formation of root- 

 lets may occur also in Dicotyledons, it may be remarked that in 

 all forms of radical fibres the vascular bundles have an arrange- 

 ment different from that in the stem, and such as would follow 

 from this mode of formation, — the fasciculi lying in the axis of 

 the rootlet, to the exclusion of the pith or cellular core which 

 occupies the central region in all the upward shoots. It may be 

 observed also, that, even in Dicotyledons, a certain vegetative 

 independence is indicated in the origin of rootlets, from the 

 local application of moisture so fostering their production as to 

 cause their development even from abnormal parts. 



It does not appear that the assumption of two distinct deve- 

 lopments of vegetative power in the guise of leaf-buds and root- 

 lets — or, as they might be termed, phyllophytons and rhizophy- 

 tons, — is at all opposed to the analogy of other forms of organi- 

 zation j for we observe a corresponding diversity of individualized 

 organs in various compound animals, as, for instance, in the 

 alimentary, generative, and protective appendages of Hydracti- 

 nia, the polypes and avicularia of the Polyzoa, and the cirrhi and 

 ovarian capsules of the Physograda, — parts which may certainly 

 be assumed to be mere modifications of a common original form, 

 but between which it would not be easy to point out much com- 

 munity of structure in proof of such co-relative derivation. 



There still remains for consideration the arrangement of the 

 dark-coloured tracts commonly regarded as of the nature of 

 woody tissue ; but for the present it may suffice to notice the 

 great diversity which prevails in different species in the disposi- 

 tion of these fasciculi. Thus, in Osmunda we have an accumu- 

 lation of dark tissue on the exterior of the caudex ; in Blech- 

 num borealej again, it occupies the interior ; in Pteris aquilina it 

 forms broad bands interposed between an outer and inner layer 

 of vascular tissue ; while in Filix mas it exists only as a thin 

 stratum ensheathing the latter ; in Lastrcea dilatata it occurs in 

 isolated masses in the cellular core of the rhizome. 



The author may remark, in conclusion, that but a few days 

 ago his attention was called by a friend to an incidental notice 

 — the only one he has yet met with — of the fibro-vascular system 

 of Ferns, in a paper on Sigillaria in the ^Edinburgh Philosophical 

 JournaP for 1844, by Mr. King of Newcastle, which, from its 

 geological title, he had previously overlooked. Mr. King's re- 

 marks, so far as they go, will be found quite in accordance with 

 the foregoing. He surmises that in Tree-ferns (owing to the 

 greater development of the longitudinal fasciculi) the regular 

 rhomboidal meshes may be reduced to long narrow slits. This 



