CULTIVATION. 401 



towers of the Now Palace at Kew (since taken down). 

 As this Fern is not found wild near London, it would 

 be useless to speculate where this solitary spore came 

 from ; it seemed however to have found a proper nidus 

 in the crevice, enabling it to germinate and resist all 

 untoward influences, to pass through the Prothallium 

 state and become a plant. 



Polypodium vulgare and Asplenium Ruta-muraria 

 may be considered our domestic Ferns ; for many years 

 a plant of Polypodium vulgare grew on the brick wall 

 separating Hyde Park from Kensington Gardens, and 

 there it remained till the wall was taken down. These 

 few instances of isolated appearances of Ferns readily 

 explain the wide geographical distribution of some 

 species over the surface of the earth. 



It has been shown that the spores of many species 

 germinate quickly and abundantly, and become fully 

 developed Prothallia, yet it often happens that no 

 plant bud is formed, and in time the Prothallia 

 decay ; the cause of this has always been supposed to 

 be undue moisture or some atmospheric action not 

 sensible to us, as this has always occurred in certain 

 species of special interest, such as Brainea insignis, 

 the spores of which, as already stated, germinate 

 readily ; yet we have not succeeded in obtaining young 

 plants, not even one Prothallium being seen to make a 

 plant bud. Without special microscopical examination 

 of the Prothallia we can only speculate on the proba- 

 bility, that, as in flowering plants, the whole of the 

 spores of some Ferns (such as Brainea) are unisexual or 

 may even be entirely destitute of both Antheridia and 

 Archegonia, in either case deficient of the elements 

 necessary for the production of a plant bud. 



2 D 



