CULTIVATION. 
401 
towers of the New 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 
tin 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 wflde 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 Protliallia, yet it often happens that no 
plant bud is formed, and in time the Protliallia 
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 Protliallia 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. 
