284 Ethel M. Berridge. 
nutritive one common to the whole, but which, as Strasburger 
suggests, have assumed in Angiosperms a new one in relation to the 
pollen-tube. 
3. The antipodal nuclei represent the nutritive and haustorial 
cells which compose the lower part of the prothallium. 
4. The upper polar nucleus represents the jacket-cells, which, 
though not as a rule capable of fertilization, yet after union with 
another nucleus, appear to be in a condition to receive stimulus 
from the contents of the pollen-tube and to proceed to the formation 
of pro-embryos. Since in the Angiosperm embryo-sac there is 
reduction to one solitary nucleus, the stimulus from the pollen-tube 
naturally takes the form of fusion with the second male gamete. 
This view of the organization of the Angiosperm embryo-sac is 
strongly supported by Dr. Lotsy’s observations on Gnetum Gnemon (7), 
although it differs widely from his own interpretation, which is 
based to a considerable extent on the exceptional case of 
Bcilanophorci. 
Drs. Coulter and Chamberlain remark in their well known 
book on “ The Morphology of the Spermatophytes,” with reference 
to the embryo-sac of Gnetum Gnemon, “ The strong polarity of the 
sac, the occurrence of naked eggs, the large or entire development 
of endosperm-tissue after fertilization, are all features suggestive of 
the Angiosperm condition. Especially striking in comparison with 
the Angiosperm embryo-sac is the occurrence of free cells at the 
micropylar end of the sac and of a compact tissue at the antipodal 
end.” When we note that this post-fertilization endosperm is 
initiated by nuclei indistinguishable from and closely related to the 
functional eggs, and commences with the formation of cells 
resembling the zygotes or pro-embryos in everything except size, 
there seems very little doubt that these are homologous with the 
jacket-nuclei of Ephedra, though Dr. Lotsy does not mention the 
occurrence of any fusions among them. From an examination of 
the figures it also appears within the bounds of possibility that the 
functional paired zygotes may be daughter-nuclei of the fertilized 
egg, which has thus far retained the tendency to divide shown by 
almost all other Gymnosperm fusion nuclei, in which case the 
second sperm-nucleus might be involved in the production of these 
weaker pro-embryo-like cells which are here called retarded 
prothallium cells. It is quite conceivable that this nutritive tissue, 
lying in close contact with the newly formed pro-embryos, would 
ultimately replace the more distant prothallial tissue at the base of 
the sac. 
