:S 
THE BOOK OF 
Finally there has been put forward as a theoretical pos- 
sibility the following plan. The archegonia, or seed-vessels, 
are as a rule situated just within the indentation of the heart- 
shaped prothallus, and the antheridia or equivalents of pollen 
masses among the root-hairs covering the larger and other half 
of the prothallus. The prothallus is most retentive of life, and 
will bear with impunity almost any amount of cutting up. We 
will therefore suppose two pans of thinly sown spores, each one 
of a different variety or species ; as soon as the prothalli are 
half grown, i.e . , before any fertilisation is likely, we take a 
keen razor and cut each prothallus across just below the 
indentation. We do this in both pans, carefully removing the 
male halves in each and neatly embedding them in the soil, 
just touching the archegonial portions of the other variety or 
species which have been left in situ, and which if deprived of 
root-hairs by the operation will certainly develop more if 
gently pressed into the soil and kept close. In this way 
the chances of self-fertilisation would be reduced to a minimum, 
and those of a cross increased to a maximum, as the subsequent 
growth of both halves would bring them into extremely close 
juxtaposition. There is, however, a good deal of irregularity 
in the arrangements of the organs on the prothallus, and hence 
this sort of division cannot be depended upon absolutely as 
separating the sexes. 
Having said so much (or so little) of the modus operandi, 
we may now glance at the results already obtained, namely, 
by simply sowing together and trusting to chance for the 
results. To Mr. E. j. Lowe must certainly be accorded the 
merits of the first most striking hybrid, viz., that effected by 
him between a cruciate form of Polystichum angulare and a 
dense form of P. aculeatum, the result being a cruciate aculeatum, 
and I may here remark that it is only where absolutely distinct 
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 choice which 
eliminate this doubt. Mr. Clapham, for instance, sowed the 
finely cut form of Polypodium vulgare, known as elegantissimum, 
with another form known as P. v. bifido-cristatum, 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 form of elegantissimum, which 
might have been a secondary sport per se, but when it tried 
to get back to normality it produced a frond of the true type 
