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i8 " - BOTANICAL GAZETTE [july 



half the chromosome representing the maternal. The germ-cells 

 would thus all be pure in regard to this character, and in self-fertiliza- 

 tion of the hybrid, according to the laws of chance the usual percen- 

 tages of a Mendelian hybrid wQuld arise. 



OTHER CYTOLOGICAL OBSERVATIONS 



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Several interesting cytological observations, a detailed description 

 of which will be presented at a later time, may be briefly stated here. In 

 the heterotypic mitosis in the pollen mother cells of the Lamarckiana 

 hybrid, the usual spHt in the chromosomes, in the anaphases, which 

 is generally described as a premature split for the homotypic mitosis 

 and is believed by many cytologists to be the reappearance of a spht 

 which occurred at the time of synapsis, occurs as described in my 

 former paper. In the early telophases, before there is any indication 

 of a nuclear membrane around the daughter nuclei or of the beginning 



w 



of a passage into the semi-resting condition, which occurs later, chro- 

 mosomes having the appearance of distinct tetrads are frequently 

 found. The indications are that this tetrad appearance, which is 

 often very clear and characteristic, may be due to the two halves of a 

 daughter chromosome (which were formed by the spHt in the ana- 

 phases of the heterotypic) remaining side by side and each becoming 

 clubbed at the ends, the portion between these ends in each remaining 

 only as a very delicate connecting thread. This gives the appearance 

 of four spherical bodies of approximately equal size, connected in 

 pairs in one direction by two parallel delicate threads. In other cases 

 the tetrads have quite a different shape, having rather the appearance 

 of a hollow ring drawn out sharply at the four comers. In still other 

 cases, in this telophase, chromosomes are seen having the shape of a 

 pair of spheres close together, or a dumb-bell, and often chromosomes 

 are found at this stage showing no indication of even a double nature, 

 but appearing univalent. This variation in form does not obscure the 

 distinctness of the chromosomes, which are usually clearly distinguish- 

 able from each other at this time, and easily counted.. AH these 

 different forms may be found together in the same nucleus, though so 

 far as observed one form usually predominates in a given telophase. 

 Figures showing these appearances will be pubUshed later. 



In the homotypic mitosis, as observed in O. Lamarckiana^ the 



