Notes . 
59i 
regarding the cytology of these new growths are still unknown ; 
it is not even certain that the cells of the aposporously produced 
prothalli possess the half number of chromosomes, and those of the 
apogamously produced sporophytes the double number, though this 
may be assumed to be probable. Apospory at least might be readily 
explainable by such a nuclear change. 
With regard to apogamy, however, some general conclusions may 
fairly be drawn even in the absence of observations on the nuclei. 
For whatever change may take place in the latter, it is certain that 
the transition from prothallus to sporophyte, or from prothalloid to 
sporophytic tissue, takes place without relation to the sexual fusion, 
and is so far comparable to an ordinary variation. Further, it is to 
be noted that the change takes place, so far as the conditions are 
known, when, by preventing the access of fluid water, fertilization 
is delayed, and when in other ways the conditions approach those 
favourable to the sporophyte rather than the gametophyte. These 
modifications of the conditions are of the kind to which aquatic 
organisms would be exposed on assuming a terrestrial habit. It is, 
therefore, possible to view the changes which take place in prothalli 
under these circumstances, not as reversions, but as indications of the 
capability of the gametophyte to assume the characters of the sporo- 
phyte under suitable conditions. If there is any truth in this way 
of regarding the facts of apogamy, they become of value in enabling 
us to picture the steps by which the Fern-sporophyte may have arisen 
by changes in individuals homologous with the original sexual form. 
The prothallus, especially in the Ferns, must have departed much 
less widely from the ancestral Algal form than the sporophyte ; this 
may be connected partly with the conditions to which it remains 
adapted, and partly with the fact of its growth being in nature cut 
short by the early formation of the embryo upon it. The various 
cases of apogamy which have been observed form an almost complete 
series of transitions between prothallus and sporophyte, and have been 
used to frame a provisional hypothesis of how the alternation in the 
Ferns might have arisen, if it did not come about in the way suggested 
by the antithetic theory. 
All such use of the facts of apogamy and apospory is liable to the 
criticism that they are teratological in their nature, and are not a safe 
guide in a morphological question of this sort. There are many facts 
which go far to justify such a view, but we should, I venture to think, 
