322 PROF. F. О. BOWER ON APOSPORY AND ALLIED PHENOMENA. 
of occurrence of apospory and its appearance (as far as yet observed) either under excep- 
tional circumstances (Mosses), or only in species of a very variable character (Ferns) 
afford strong evidence that the exchange is not a real advantage to the plant; if the 
excision of the sporal stage from the cycle of life were a decided gain, we might well 
have expected to find the peculiarity to be not only common but also permanent *. 
It isa striking fact that in one of the aposporous Ferns (Polyst. ang., var. pulcherrimum) 
prothalli are formed on the fronds while they are still erect; further it is to be 
remembered that in my first observations on the prothalli of this Fern, neither 
antheridia nor archegonia were in a position to effect the sexual process, since neither 
had opened f: presumably this is to be ascribed to their not having access to fluid 
water; this must often be the case with prothalli produced early on the erect fronds: 
thus, in this instance, the delay before effecting sexual reproduction, as well as the 
smaller number of oophores produced, must be set against the advantage of greater 
security of nutrition ; it is difficult to see how any balance of advantage from apospory 
could remain to this plant. In the Athyrium F.-f. var. clarissima the case is clearer; 
this Fern is deciduous, and when the fronds reach the soil, the same processes may 
promptly be gone through in nature as have been observed in the cultures in the labora- 
tory: thus, in this case, it is only by the production of a smaller number of oophores 
that the plant loses, while it gains in the certainty of their nutrition in early stages. It 
has been already noted that these two cases of apospory in Ferns are found in varieties | 
of very variable species 1; if the above conclusions be correct, it is among deciduous 
rather than evergreen Ferns that further examples of apospory are to be anticipated, 
and especially in those deciduous species which are most subject to variation. 
Already the observations of Pringsheim and Stahl have had their effect in demon- 
strating that no fixed and impenetrable barrier exists between the sporophore and the 
oophore; in fact, that the formation of spores is not a necessary stage in the cycle of 
life in isosporous forms. "This conclusion is greatly strengthened by the above obser- 
vations on aposporous Ferns; and the more so that both the present examples are 
natural, and not brought about under the stress of artificial circumstances. It is now 
clear that the Fern prothallus may grow out from characteristic tissues of the sporo- 
phore, and, further, that where apospory occurs, it does not necessarily originate from a 
single cell, which might thus be taken as representing the spore, but from a number of 
cells, there being no sharp limit between the characteristic sporophore and the charac- 
teristic oophore. A further question which here suggests itself is this: Are these 
phenomena of apospory to be regarded as mere sports, or as having a deep morphological 
meaning, and throwing light upon the origin of the two distinct generations? To me 
the former interpretation seems the more in accordance with the facts; it is to be 
* Mr. Druery tells me that signs of reversion to the normal type are to be found in Polyst. angulare, var. pul- 
manas, Col. Jones's impression that Athyr. Е.-}. var. clarissima did not, when first found, present the pecu- 
liarities now described may also be noted. 
+ Journ. Linn. Soc., Bot. vol. xxi. p. 363, also plate xii. figs. 11, 12. 
+ Compare Lowe (‘ Our Native Ferns ), Who describes over 100 varieties of Polystichum angulare, and more 
than 200 varieties of Athyrium Filix-femina. | 
