a Se 
CANNON: Stupres in PLranr Hyprrips 157 
ture of a hybrid may be of considerable use in determining the 
relative independence of the germ-nuclei. 
I wish now to turn from the considerations of nuclear divisions 
and hybrid variations and apply ¢heoretically the principle of the 
purity of the sex-cells to a moss, a fern, and a seed-plant. In 
doing so I assume, as a matter of course, that the hypothetical 
hybrids are monohybrids of the Péswm-type. The theoretical 
application is made rather to call attention to what seems to me a 
very broad and inviting field for research, than to attempt at this 
time any development of the field myself. Many additional points 
of view will undoubtedly suggest themselves at once to any botanist. 
We shall consider what happens when one sort of a moss is 
crossed with another sort, when the spores of the hybrid moss 
develop, and, finally, when the hybrid is inbred. 
In the first place when a moss is fertilized by the sperms of a 
moss of another species, the moss “ plant” is not hybridized, since 
the effect of the foreign fertilization is to be observed only in the 
Sporogonium. This applies to the hybrid of the first generation ; 
what happens in the later generations has apparently not been 
studied or at least recorded. Focke (/. c. 427) says that no hybrid 
sexual moss plants (gametophytes) have been recognized, and he 
inquires if some of the numerous sterile mosses may not be hybrid. 
According to the hypothesis of the purity of the spores we should 
not expect to find hybrid gametophytes in any generation. And in 
this connection it is certainly interesting to note that there is said to 
be no hybrid among the liverworts. This again would be the case 
if the spores from which the liverwort “ plant’ arises are not 
hybrid but pure, and we may perhaps make the rule that z¢ zs the 
sporophyte, and not the gametophyte, which ts of hybrid BOURT. 
Assuming the purity of the spores, when the hybrid is inbred 
variation of the sporogonia would occur according to the law of 
Mendel, but not necessarily according to the Pisum-ty pe. ‘Tae 
variation of the hybrid will depend on the monoecious or dioecious 
nature of the moss. This will be clear when we examine the for- 
mulae for variation of monoecious and of dioecious ferns. 
Turning now to the fern hybrids, we shall rst. consider a 
monoecious homosporous hybrid, and, finally, a dioecious homo- 
sporous hybrid. 
