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THE AMERICAN NATURALIST [Vol. XLIV 



fourths), so that one-half of the normal number of pollen grains 

 appeared. Here, again, it is the period of synapsis or of con- 

 jugation of the maternal and paternal chromosomes (the stage 

 corresponding to the gametophyte, where the chromosomes are 

 reduced in number) where the effects of hybridization are 

 evident. 



Juel 21 has shown that the chromatin distribution in the nuclei 

 of hybrids is irregular, corresponding to the conditions in hybrid 

 animals described earlier in the present paper. The condition 

 of the chromosomes during actual synapsis is such that it is 

 impossible to observe their behavior directly and, doubtless, noth- 

 ing could be learned of the ultimate cause of the irregularities 

 through mere observation during these periods, even if the 

 chromosomes could ho more clearly followed. In such cases, it 

 seems to me, we have fought the matter of sterility to its inner 

 keep, and until experimentation comes to our aid, Ave shall be 

 able to proceed no farther. "Uber die Art und Weise, wie die 

 Eizellen steril werden, haben wir keine erwahnenswerthen An- 

 gaben gefunden" (DeVries). 



Several cytologists have taken advantage of the exhaustive 

 studies of DeVries upon hybrids of the primrose, Oenothera 

 lamarcTciana, to study the cellular phenomena of crosses whose 

 general features are well known. Thus, Geerts 22 has recently 

 studied the partial sterility and the development of the embryo- 

 sac of (Enotha-a and finds that there are no antipodal cells de- 

 veloped and that the endosperm forms from the pole cells. 

 Sterility, says Geerts, is a matter of irregularities in the reduc- 

 tion division and therefor.' his observations tally with those, both 

 plant and animal, spoken of above. 



Gates 23 and Miss Lutz 24 have investigated the cytology of (Eno- 

 thera crosses and of Drosera hybrids. Irregular distribution of 

 the chromosomes obtained in the reduction division and these 

 differences are correlated with the external characters of the 

 crosses. 



"Juel, H. O., "Beitriige zur Kenntnis dor Tetradentheilung, " Jahrb. 

 wiss. Bot., Bd. 35, 1900. 



"Geerts, J. M., "Recueil Trav. Bot. Neerl.," T. 5, 1909. 



"Gates, R. R., Bot. Gaz., Vols. 46 and 48; Science, Vols. 27 and 30; 

 ArcMv fur Zellforsch., Bd. 3, H. 4, 1908-09. 



u Lutz, Annie M., Science, Vol. 29, 1909. 



