﻿Hance : Pollen development in Zebrina pendula 



theras which were sterile and has reviewed a number of other cases 

 (4) . The two germ plasms of Guyer's hybrid pigeons were found 

 to remain separate in the cells of the testes. Speaking of a large 

 chromosome appearing on the spindle as four small rings or 

 vesicles, he says: " It is possible that* this indicates a demarcation 

 into tetrads, visible in hybrid material because of the firmer 

 fusion which occurs normally at this stage is lacking. ... It 

 simply means, that in all probability there is an incompatibility 

 between the chromosomes from the two dififerent species which, in 

 some cases, prevents them from uniting for the pseudo-reduction 

 that normally occurs at this time." He also finds that " the 

 division may be such that a portion of the chromatin is cut out 

 entirely and is left behind in the cytoplasm." (5.) 



Miyaki (6) states that the reduced number of chromosomes in 

 T. virginica is twelve while Farmer and Shove claim the number 

 to vary between twelve and sixteen. In the present study the 

 number has been found to range between twelve and fifteen. 



Mottier (7) states that the chromosomes of Tradescantia 

 virginica arc arranged in pairs and that in the first division they 

 may be attached end to end so that as they are drawn apart rings 

 may be formed. Each half that goes to the poles soon appears to 

 be paired and remains in that condition until the second division, 

 when the members of the pair separate. This differs from the 

 case reported in the present article in that the pairs in Zebrina 

 pendula behave as single chromosomes right through the first 

 division and no evidence of a second longitudinal division has 

 been observed. 



The great difference between somatic and germinal chromo- 

 somes would seem to point to the fact that chromosomes are 

 influenced by the chemistry of the cell. The writer has observed 

 a difference in the chromosome number of the somatic and germ 

 cells of the pig and in another paper has discussed the importance 

 of chromosomes in heredity from this point of view. 



Botanical Laboratory, 



University of Cincinnati 



