132 Bower . — Is Eusporangiate or Leptosporangiate 
logical phenomenon, and not as a reversion. If, however, 
the views as to the origin of the antithetic alternation, 
which I have elsewhere put forward, be accepted, and also 
that the Eusporangiate Ferns be really primitive, apospory 
appears in a new light : as at present recorded it is found to 
occur in Leptosporangiate Ferns and Mosses; in forms which, 
under the present hypothesis, are specialised in accordance 
with a moist and often shaded habitat ; in these the circum- 
stances of life on exposed land surfaces, which in my view 
conduced in the first instance to the antithetic alternation, 
are mitigated : living, as at least many of the aposporous 
plants do, in an almost uniformly moist habitat, it is to be 
expected, rather than wondered at, that the limits of the 
alternate generations should be obliterated : that the typically 
terrestrial sporophyte should, on exposure to surroundings 
more specially favourable to the growth of the gametophyte, 
grow out directly into the prothallus : and that the spore- 
formation, which is the distinctively sub-aerial mode of 
propagation, should be in abeyance: more especially is this 
to be anticipated in the Hymenophyllaceae when grown in 
closed cases ; and what more pronounced example of apospory, 
of actual obliteration of the limits of the two generations, 
could be afforded than that of Trichomanes alatum 1 ? The 
very existence of apospory in Leptosporangiate Ferns seems 
to me to support the view that they are derivative and 
specialised forms rather than primitive, and these remarks will 
apply equally to the Mosses, in which aposporous development 
is induced only under conditions of specially damp culture. 
In the above pages it will, I think, have been sufficiently 
shown that the view of the Eusporangiate Ferns as relatively 
primitive is capable of defence : a comparison of form and 
development, the palaeontological evidence, and even the 
facts of apospory, all fall in with this theory, and give it more 
or less uniform support ; but it is impossible at present to do 
more than put it forward as an hypothesis, and the question 
must still be held to be an open one. If the new view be 
1 Annals of Botany, vol. I, p. 278. 
