Farmer. — On the Structure of a Hybrid Fern. 539 
amount of variability amongst the purpureus lot, expressly 
mentions the fact that a purple colour was sometimes present 
on the flower-stalks of seedling-plants which otherwise would 
be referable to C. Laburnum. The fact that the reversion to 
the parent form in C. Adami is both more perfect and also 
seems to be accompanied by a corresponding increase in 
fertility, when compared with the state of things present 
in P. Schneideri , does not in any way affect the legitimacy 
of instituting a comparison between these two plants ; but 
rather adds to its interest. 
Although the reversion on the part of the Polypody is 
commonly in the direction of the vulgare type, indications 
are not wanting, as has already been stated, that the aureunt 
form may also reassert itself ; and in the Cytisus it is usual 
for one (commonly the Laburnum) parent to manifest itself 
before the other. The extreme sterility of the hybrid type 
in both cases is of special interest when contrasted with the 
known fertility of the reverted portions of Cytisus and their 
possible fertility in the Fern. Even should the spores of the 
latter prove not to be germinable, they are, as microscopic 
examination shows, far less hopelessly barren than are those on 
the hybrid plants, and they are immeasurably more numerous. 
Of course it may be argued, as has already been hinted, 
that the sterility of the hybrid leaf is not necessarily a con- 
sequence of its hybrid origin, but is merely correlated with 
the foliar expansion, just as the leafy sterile part of an 
Osmunda frond is said to be when compared with its con- 
tracted fertile part. And it might be urged that, on my own 
showing, the dissected fronds of P. elegan tissimum are not 
so sporangiferous as are those which have assimilated them- 
selves to the vulgare type. But the first argument, even 
if the premises be admitted, is not to the point ; and with 
regard to the second, it may be said that we are thereby 
brought no nearer to accounting for the absolutely sterile 
nature of the hybrid spores, whether the sori are produced in 
abundance or not, and this peculiarity must, I think, depend 
on some intimate change in the configuration or composition 
