APOGAMY AND APOSPORY 57 
well ask whether such an interpretation does not read into the facts more 
than actually exists? If Zsce¢es were a plant which habitually showed 
combined apospory and apogamy, and if various steps were present leading 
towards the extreme result, then the conclusions might be accepted. But 
fsoetes is'a plant which is structurally stable as a rule, and there is in 
these abnormal growths no prothalloid tissue at all. Thus they appear to 
be merely sporophytic buds formed from sporophyte tissue, and having 
sporophytic character throughout. They will rank with those sporophytic 
buds which are found arising from the sorus in various Ferns, or from 
the nucellus in some Phanerogams: they are, in fact, a mode of vegetative 
continuance of the neutral generation, and nothing more. 
The question necessarily presents itself, what is the cytological state 
of the tissues in the plants which. show those vegetative transitions from 
one generation to another, such as have been described for the Mosses 
and Ferns above named? The facts would appear to be inconsistent with 
the structural distinction of the two. generations, since the acts of sexuality 
and of spore-formation, by which the cytological changes are normally 
effected, are liable to be omitted. It will be important to know how 
far the distinction between the haploid and the diploid phases will remain 
valid. The facts have lately been elucidated for a number of the 
abnormal Ferns by Prof. Farmer and Miss Digby,! and for the very 
peculiar case of the genus Marsilia by Prof. Strasburger.? 
Taking first the case of apogamy: already in 1898 Dr. Lang had observed 
in prothalli of Scolopendrium, in the tissues bordering on the change 
from gametophyte to sporophyte, the frequent presence of two nuclei in a 
single cell (Fig. 36). More detailed observations have since been made on 
other apogamous Ferns, by examination of very young prothalli, before any 
apogamous growths had begun to manifest themselves.’ Similar cells with 
two nuclei were observed in the case of prothalli of Lastraea pseudo-mas, 
var. polydactyla ; but it was shown that when two nuclei are seen in a single 
cell a neighbouring cell is without one, and cases were found where the 
passage of the nucleus through the cell-wall was actually in progress 
(Fig. 39). This process is regarded as a kind of irregular fertilisation, 
for ultimately the two nuclei fuse. On their division the nuclei of the 
apogamous growth thus produced show, as a consequence of the fusion, 
evidence consistent with a doubling of the chromosomes, just as it 
happens in the normal post-sexual stage. But instead of one cell only 
serving as the starting-point for the new generation, a number of such 
units co-operate loosely to produce it. These results have their interesting 
bearing on the irregularity of number, and the sporadic position of the 
parts in such cases as those observed by Lang. It is thus seen that even 
in these irregular examples the cytological criterion: between the two 
generations may hold, and the structural limit will be found in the cells 
l4nn. of Bot., xxi., p. 161. : 2 Flora, 1907, p. 123. 
3 Farmer, Moore, and Digby, Roy. Soc. Proc., \xxi., 1903, p. 453- 
