METAMORPHOSIS. 



201 



resemblance to virescent ovules of the small marginal 

 ascidia in the foliage-leaf of Saxifraga crassifolia 

 observed and figured by Goebel and Massolongo. It 

 is clear that some of the virescent ovules are also 

 ascidia of exactly the same form and position. 



Exact homologues both of the metamorphosed ovule 

 and of the unaltered ovule or " ovular leaflet " may be 

 found as normal structures in other departments of the 

 vegetable kingdom. Celakovsky finds such in the ap- 

 paratus of the female " flower " of the Coniferse. The 

 Taxacese present the instance of the normal ovule along 

 with its two integuments ; the remaining groups that 

 of the semi -proliferated ovule, of which the seminiferous 

 scale (or rather one-half ther.eof, seeing that each scale 

 possesses two ovules) is the vegetatively-developed 

 outer integument bearing the involuted nucellus- 

 producing inner integument on its lower (dorsal) 

 surface. The case of Oupressus, . in which a single 

 seminiferous scale bears several such inner integuments 

 on its lower surface, finds its counterpart in Hesperis, 

 as we have seen ; such a structure as this might con- 

 ceivably arise out of a compound ovular leaflet, the 

 terminal segment of each lobe becoming, as in the 

 simple trilobed leaflet, the inner integument borne on 

 that lobe's lower surface. Descending lower in the scale, 

 precisely the same set of structures (although naturally 

 modified in accordance with the idiosyncrasies of the 

 special group of plants in which they occur) are exhibited 

 as normal stages of development in the sporophylls 

 of the ferns. In Thyrosopteris and Hymenophyllacese 

 we see the case of the normal or slightly leafy ovule of 

 Angiosperms and of Taxaceaa, in which the receptacle 

 bearing its numerous sporangia (homologue of the 

 nucellus), terminal in position, is en sheathed by the 

 integuments, of which the indusium is the morphological 

 equivalent of the inner, while the outer integument is 

 represented by the laminar extension (when present) 

 of the pinnule-segment on either side of the indusium. 

 If now this structure be compared with the virescent 



