certain Penaeaceae . 
373 
writers even consider that the four nuclei formed by the reduction division 
should be always regarded as the nuclei of four spores, whatever may 
be their subsequent history . 1 The gametophyte of plants, normally a 
post-meiotic phase , 2 is to be regarded on this view as always post-meiotic, 
the number of cell-generations in it corresponding to the number of post- 
meiotic divisions of these four nuclei. 
This view has lately been elaborated for the embryo-sac of the angio- 
sperms by Coulter , 3 who applies it to all cases in which the mother-cell 
divides only once, or else functions directly as the embryo-sac ; and there- 
fore in which, according to him, two spores in the first case, and four 
in the second have been involved in forming the embryo-sac. That this is 
probably the case in Peperomia has been shown by Brown , 4 who describes 
the formation of evanescent walls or cell-plates between the first four nuclei 
of the embryo-sac in the species he has studied. Though careful search has 
discovered no signs of such walls or cell-plates in the first divisions of the 
macrospore mother-cell in the Penaeaceae, the absence of a row of mega- 
spores, combined with the tetrahedral arrangement of the first four nuclei 
formed, makes it seem possible to the present writer that the peculiarities 
of the embryo-sac may here also be best explained by regarding it as 
a specialized type, in the development of which all four megaspores have 
become included, the germination of each ceasing at the four-nucleate 
stage. Some similar cases of four potential megaspore nuclei being 
included in a single cell (only one, however, germinating) are cited by 
Brown . 5 Evidence on this point is unfortunately wanting in Euphorbia 
procera , since Modilewski’s material showed nothing earlier than the four- 
nucleate stage. If the early stages of development in this form should 
prove to be the same as in the Penaeaceae, it is probable that the two may 
be regarded as cases where specialization has proceeded on parallel lines. 
Whether the embryo-sac of these Penaeaceae is to be regarded as 
a relatively primitive one, or as one which has been reduced and specialized 
in the manner suggested, two explanations of its structure will still both be 
applicable. One of these has been advanced by Ernst, who applies to the 
Penaeaceae 6 the homologies suggested by Porsch 7 as an explanation 
of the embryo-sac and double fertilization in the angiosperms. Porsch 
interprets the egg-apparatus as being homologous with a Gymnosperm 
archegonium, the synergids representing the neck cells , 8 and the antipodal 
cells as being equivalent to another ‘ sexually-degenerate ’ archegonium. 
1 Davis, 1905, pp. 471-2. 2 Farmer and Moore, 1905, pp. 548-9. 
3 Coulter, 1908. 4 Brown, 1908. 
5 ibid., pp. 453-4. 6 Ernst, 1908 (A), p. 434 ; 1908 (B), p. 33. 
7 Porsch, 1907, pp. 19, 20. 
8 Chamberlain (Bot. Gaz., xlvi, p. 155, 1908) and Went (1909, p. 13) interpret Porsch as 
holding the synergids homologous with neck canal cells, but this seems a misinterpretation of 
Porsch’s view. 
