158 THE THEORY OF THE GENE 



tetraploid. This hybrid between these two widely differ- 

 ent species is, according to earlier observations, sterile, 

 but fertile according to other observers. 



In the maturation stages of the germ-cells, few or even 

 no conjugating chromosomes were observed, as shown in 

 the next table : 



The distribution of the chromosomes to the poles is 

 very irregular; few if any of the singles divide before 

 reaching the poles ; some of them are left scattered in the 

 cell. In the second division many of the chromosomes 

 split, but those that divided in the first division lag and 

 pass slowly to the pole ; the number that lag is, however, 

 much less than in the first division. 



The almost complete absence of conjugating chromo- 

 somes in the cross between wheat and rye is the most 

 interesting feature of the cross. The resulting irregu- 

 larity in the distribution of the chromosomes mil prob- 

 ably account for the generally observed sterility of the 

 hybrid. There is a possibility that all the chromosomes 

 (or most of them) belonging to one species might, as a 

 rare event, pass to one pole. This might lead to the for- 

 mation of a functional pollen grain. 



The Polyploid Roses. 



Since the time of Linnaeus the classification of many 

 of the roses has baffled the skill of taxonomists. The re- 

 cent discoveries of a Swedish botanist, Tackholm, and of 

 three English botanists, Harrison and Blackburn in 

 collaboration, and Hurst, a rose expert and geneticist, 



