210 BOTANICAL GAZETTE [SEPTEMBER 
produced. This one, however, never passes out of the egg, but 
after migrating a short distance its nucleus returns to the egg 
nucleus and fuses with it, thus restoring the diploid number of 
chromosomes. BLACKMAN (2) believes that the nuclear fusion 
occurring in the aecidium of Phragmidium is a “reduced form of 
fertilization.”” The fusion of two gametophytic nuclei in D. 
gracile is indeed quite comparable to the union of the nucleus of 
one prothallial cell with that of another in Lastrea pseudo-mas 
var. polydactyla Wills, which FARMER and Dicsy designate as 
pseudo-apogamy. They state: . 
We would suggest the term pseudo-apogamy to cover instances in which 
the sexual fusion of gametes is replaced by a fusion of ordinary gametophytic 
nuclei which morphologically are not sexually differentiated. This would in- 
clude the process as it occurs in the Uredineae and probably the Ascomycetes, 
and also the growing number of instances of apogamy in prothallia induced 
by cultural conditions, as well as such cases of obligate apogamy as that of 
the polydactyla varieties of the male fern. 
According to them, conjugation of adjoining cells of the same 
filament in Spirogyra might be looked upon as examples of an 
analogous phenomenon. Whether the nuclei which fuse in D. 
gracile, in Lastrea pseudo-mas var. polydactyla Wills, and in Spirogyra 
really are undifferentiated morphologically is not definitely known. 
The gametes of S pirogyra or Mucor, for example, are believed to be 
morphologically alike. Aside from the fact that they are sometimes 
produced on different individuals, does not their conjugation con- 
stitute a process essentially like the examples just mentioned? 
Physiologically the gametes of Spirogyra and Mucor are believed 
to differ distinctly from each other. So in D. gracile, the author — 
regards the two gametophytic nuclei which conjugate as potentially 
different from each other and from all other nuclei in the game 
tophyte. Externally they are alike. Therefore, may not their 
fusion constitute a process essentially like that of the conjugation 
of the gametes in § birogyra? The union of the gametophytic 
nuclei in D. gracile does not result in the mixing of parental charac- 
ters from separate individuals and does not constitute a true sexual 
process in this respect. Their fusion results in doubling the number 
of chromosomes and furnishes a stimulus to further development. 



