276 REPORT OF THE CONFERENCE ON GENETICS. 
would submit to an alliance, the generic difference being a minor one. 
So with the Nephrodiwm family and the Asplenia, in which latter con- 
nection, though the genus generally appears to consist of very constant 
species, one of our species, Aspleniwm Trichomanes, has sported freely and 
prettily, and since difference in size of ferns presents no obstacle to inter- 
crossing, here again is an extensive genus open as a working field. The 
hartstongue, too, is so closely allied to the spleenworts that already two 
well-established cases of hybridisation are recorded, and judging by the great 
similarity of type the gigantic Asp. nidus avis might easily be induced 
to combine with some of the fertile frilled and tasselled hartstongue, 
to the hardening of its constitution and the diversification of its form. 
In this connection it must be borne in mind that combined sowings 
should only be made with spores of really fine varieties and to some 
definite end. The élite of our British ferns should be chosen as possible 
mates for fine exotic normals. It is just as easy to start on the “best” 
lines as on inferior ones. Thoroughly constant and symmetrical varieties 
should alone be used, and as the spores of different species vary consider- 
ably in their time of germination and maturation of the prothallus, some 
experience would have to be gained in order that the two sowings might 
be made at such periods that the maturation of both should be approxi- 
mately simultaneous. In such cases, of course, the first sowing of the 
slower germinator would require to be a thin one. The spores should 
always be sown on soil carefully sterilised with boiling water, and after 
sowing the pot or pan should be continually covered with a piece of glass 
or a bell to exclude the subsequent deposit of stray spores or inimical 
germs ; particular care must also be taken to exclude worms, since a 
single worm, even a small one, can ruin a crop by disturbance. As an 
alternative to successive sowings, it has been suggested, and indeed we 
believe Polypodium Schneiderti was acquired in this way, that the sowings 
be made in separate pans, and mature prothalli picked out from each and 
inserted side by side, touching each other, in separate pairs. A point in 
favour of this mode is that spores, even of one and the same species or off 
the same frond, vary in speed of development, some maturing much more 
rapidly than others, so that there is often a succession of young plants for 
a considerable period; and another point is that, assuming careful 
sowing and fairly pure culture, the resulting couple of prothalli are bound 
to be of the two kinds, and in this way it might be even possible to 
determine the maternal or paternal relations of the offspring, which by 
joint sowing is impossible. The maternal parent is of course the fern- 
producing prothallus, while the paternal one would be the other, always 
assuming that the offspring proves to be a hybrid; if not, it must be 
assumed that no cross has taken place, but-that the two elements of the 
same prothallus combined. The risk of antecedent fertilisation cannot 
well be prevented, as the antheridia, or male cists containing the anthero- 
zoids, are usually scattered too much over the under side of the prothallus 
to be eliminated by any process of division such as has been suggested. 
It may be mentioned here that the prothallus is extremely tenacious of . 
life and bears shifting, and even division, with impunity under congenial 
conditions of growth. So much for cross-fertilisation and the field open 
for its exercise in conjunction with the rich material the British species 
