FERN CROSSING AND HYBRIDISING. 291 
forms such as these are crossed that we can be sure that the progeny is 
a cross at all, because once a fern or other plant has broken away from 
the normal plan of growth, its progeny is apt to vary again, probably 
more or less on the same lines, but not necessarily so. Fortunately, 
however, numerous crosses have been effected under circumstances of 
P. y. ELEGANTISSIMO-CRISTATUM (A+B). 
A+B 
108.—Ponypoprum VULGARE BreIDO-crIsTaTUM (A) x P. vy. ELEGANTISSIMUM (B). 
C shows a frond of the cross A +B reverting to one of the parents A, and not to the normal form. 
Fia. 
choice which eliminate this doubt. Mr. Clapham, for instance, sowed 
the finely cut form of Polypodiwm vulgare, known as elegantissimum, with 
another form knownas P. v. bifido-cristatwm, an attenuate crested form. 
Elegantissimum-has a peculiar knack of partial reversion to the normal. 
The offspring of the cross was not merely a more or less tasselled 
v2 
