12 Proceedings. ' 



—that is, parasites within the individual cells of the body. More experi- 

 ments, larger knowledge and improved technique may, however, soon re- 

 move this apparently insurmountable barrier. 



Recent views concerning the embryo-sac of Angiospernls 

 and the cells produced by it, by Professor Conway Mac- 

 Millan. 



[abstract.] 



Current discussion concerning the homologies of the Metaspermic em- 

 bryo-sac is somewhat clarified by recent papers of Guignard, Hartog, Bret- 

 land-Farmer, and others. The notion that the endosporic cells are not 

 in the nature of a female gametophytic plant has been again argued by 

 Guignard, upon the bases of his researches concerning the number of chro- 

 matomeres in theequatorial plane of vegetative and reproductive nuclei. This 

 view has already, from other morphological evidence, been advanced by 

 Warming, Vesque and Mann, but is, on the whole, not to be credited be- 

 cause of the distinct homologies with the embryo-sac of Archispermous 

 plants, like Cycas, where the embryo-sac is clearly a megaspore, and on 

 account of other and simple explanations of the number of nuclear seg- 

 ments in the definitive nucleus of the sac before the divisions of germination. 



Considering the embryo-sac in all cases then, as a spore and not as a 

 special spore-mother-cell, it becomes evident that the traditional explana- 

 tion of the seven cells which are produced within it in the Metaspermae is 

 not far from the truth. They represent a degraded and symbiotic sexual 

 plant, forming the female of the same generation as that in which the 

 pollen-tube is the symbiotic male. 



The older view that the antipodal cells represent the prothallium of the 

 female plant is, however, not to be maintained, and in evidence the results 

 of certain examinations of different pollen-tubes and embryo-sac contents 

 were adduced. It will be found that in the case of iVarc/ssus, Cwcurfoita 

 and others, the staining of the second polar cell of the egg and that of the 

 sperm nucleus is similar in all points, and that in structure, size and reac- 

 tions to safranin, dahlia and other dyes, these nuclei are readily compar- 

 able. On the other hand, the antipodal cell that migrates to the top of the 

 embryo-sac, where it finally fuses with the second polar cell of the egg, 

 otherwise known as the micropylar endosperm-forming nucleus, is compar- 

 able more directly with the other micropylar cell which is universally recog- 

 nized as having the character of an egg. In size, structure and chemism, 

 these cells are similar. It therefore appears that the antipodal cells, as is 

 determined by Hartog, upon a purely theoretical basis, are experiment- 

 ally seen to have the character, not of prothallium, but of an archegonium, 

 and the embryo-sacs of Metaspermae are universally characterized by the 

 production of two eggs. One of these is cross-fertilized by the sperm nucleus 

 of the pollen-tube, and develops the embryo of the seed. The other is close- 

 fertilized by the polar body of the micropylar egg and develops a dependent 

 sporophytic plant, the endosperm, and this is destroyed, either during pro- 

 cesses of seed-ripening or of seed germination, in both of which it comes into 



