i 70 Berridge and Sanday. 
fusing jacket-cell nuclei may be sexual in nature; if so, a parallel 
can be drawn, perhaps, still more closely with those cases among the 
Uredineae, where fertile cells have been shown by Christman and 
Mr. V. H. Blackman to fuse in pairs before giving rise to the 
jecidiospores (11). The fact that it is the pro-embryos in and 
adjacent to the archegonia which seem to have the best chance of 
forming embryos, raises the question whether the contents of the 
pollen-tube play any part in this method of embryogeny. The 
number of archegonia to which no pollen-tubes have found their 
way are comparatively few ; in cases where tubes have undoubtedly 
entered, sometimes there is total failure to produce pro-embryos, 
usually owing to the disintegration of the egg-nucleus, and some¬ 
times the “abnormal” series of pro-embryos is found. It seems 
quite possible that in these latter cases the contents of the tube 
may stimulate the jacket-cell nuclei to further development, or 
that some of the nuclei from it may fuse with them. In one 
instance this seems about to occur, a jacket cell nucleus being 
found in the act of breaking through into the egg-cell, close to one 
of a group of four pollen-tube nuclei lying in the apex of the 
archegonium ; as yet no other jacket nucleus has escaped into the 
egg-cell. It is evident, however, from the number of pro-embryonal 
cells formed actually within the jacket cells that the direct stimulus 
of fusion with a pollen-tube nucleus is not essential to this 
development of pro-embryos. 
Although this mode of embryogeny has been called abnormal, 
and regarded as possibly the result of adverse conditions, yet it 
seems not improbable, as far as can be gathered from M. Jaccard’s 
account of embryo-formation in E. helvetica (2), which is not at all 
clear on many points, that the same kind of apogamy occurs in that 
species also. He speaks of the renewed activity of the jacket cells 
after the time of fertilization, and of the occurrence of mitotic 
division and considerable growth at that period, and remarks on 
the great likeness to small archegonia which they present. He 
aments the impossibility of distinguishing between certain “conden¬ 
sations protoplasmiques globuleuses” and the true daughter-nuclei 
of the fertilized egg-nucleus, and mentions in passing that these 
condensations are surrounded by definite zones of cytoplasm. These 
are probably the young pro-embryonal cells formed by the escaped 
jacket-nuclei. The young embryos which are described as arising 
directly from the pro-embryonal cells without any formation of 
tubular suspensors are spoken of as occurring amidst a tissue of 
