244' WALTER S. SL'TTON. 



a maternal chromosome fuse permanent!}' to form a new chromo- 

 some which subsequently divides only equationally. The result 

 must be germ-cells which are identical with one another and 

 with those of the parents, and hence self-fertilization would pro- 

 duce offspring practically without variation. If this explanation 

 be the correct one the process is distinctly pathological and 

 hence it is not surprising that such cases, as noted by Bateson, 

 should often present "a considerable degree of sterility." 



3. The " False Hybrids " of Millardct. - - Millardet, de Vries 

 and Bateson have all described experiments in which the offspring 

 resulting 1 from a cross between dissimilar individuals showed the 



o 



character of one parent only, those of the other parent being 

 shown by further experiment to be lost permanently. The 

 obvious cytological explanation of such a phenomenon is hinted 

 at by Bateson in the words " Such phenomena may perhaps be 

 regarded as fulfilling the conception of Strasburger and Boveri, 

 that fertilization may consist of two distinct operations, the stimulus 

 to development and the union of characters in the zygote." Divi- 

 sion of the egg without fusion of the pronuclei in a well-known 

 phenomenon having been observed in eggs treated with chloral 

 (Hertwig brothers) or ether (Wilson) and may be supposed to 

 occur under certain unusual conditions in nature. In the ex- 

 periments mentioned, however, both pronuclei continue to divide 

 separately, while for a cytological explanation of the occurrence 

 of " false hybrids " it is necessary to conceive not only the failure 

 of the nuclei to copulate but the entire disappearance of one of 

 them. Such a case would be comparable to that of chemically 

 induced parthenogenesis or to the fertilization of enucleate egg- 

 fragments, according as the nucleus remaining was maternal or 

 paternal. Speculation in this connection, however, is unprofit- 

 able excepting so far as it may serve as a guide to research. A 

 careful study of the fertilization of such cases as Millardet's 

 strawberries, de Vries's Oenothcra and Bateson's Matthiola crosses 

 will no doubt be productive of immediate and positive results. 



Mosaics. A fourth class of non-Mendelian cases, the 

 " mosaics " or " piebalds ' constitute a group in relation to 

 which, as I believe, only negative evidence is to be expected 



1 Bateson and Saunders, he, cit., p. 154- 



