142 



THE BOOK OF CHOICE FERNS. 



Finally, we extract from a paper by Professor Bovver with reference 

 to Mr. Druery's observation, which was read at the Linnean Society's meeting 

 on the 18th December, 1884, the still more interesting example of Apospory 

 of which Mr. Gr. B. Wollaston is the discoverer, and which bears on the plant 

 already mentioned, Aspidium (JPolystichum) aculeatum angulare jndcherriminn. 

 " Here," Professor Bower says, " flattened organs, of undoubted prothalloid 

 nature, are formed by simple vegetative outgrowth of the tips of the pinnules, 

 and without any connection with sori or sporangia. At first the tip of the 

 pinnule merely extends, so as to form a flattened expansion, one layer of cells 

 in thickness, and with a very irregular margin ; while the whole tip curves 

 downwards, and often forms a spiral coil of one or one and a-half turns, closely 

 covered above by the more expanded portion of the pinnule. In other cases 

 the outgrowth may assume very irregular forms. Ultimately the characteristic 

 marginal growth begins at some point, sometimes terminal, but more frequently 

 lateral," &c. This latter instance, being an example of the formation of an 

 expansion of undoubted prothalloid nature, bearing sexual organs, by a process 

 of purely vegetative outgrowth from the plant, may be considered as a still 

 more complete example of Apospory than even that of As-plenium Filix-ftiemina 

 Clarissima. 



From the preceding remarks, which have been derived from Mr. Druery's 

 excellent work on " Choice British Ferns," in which the process of Apospory 

 is very minutely described, and to which the reader may refer for more 

 detailed particulars, it wull be seen that no less than three distinct forms of 

 proliferation have now been observed in the Athyrium section of the genus 

 Asplenium : 



(1) Bulbils of the ordinary character, developed in the axils and on 

 the superior surface of the pinnae, and agreeing in general characters with the 

 ordinary bulbils of Asplenium. 



(2) Bulbils formed apparently by transmuted spore-producing energy, and 

 occupying the place of sori, i.e., on the under-side of the pinna? — a position until 

 now, we believe, quite unrecorded in connection with any of the Filices. 



(3) A new form of proliferation altogether, viz., proliferous prothalli 

 arising from pseudo-bulbils produced by a different transmutation of the repro- 

 ductive force, and evolving plants only after the prothalli have produced the 

 usual sexual organs common to prothalli resulting from spores. 



