212 BOTANY 



generations the A type bred true, B plants produced B and A, 

 and Bj families bred true. Further, when the A and B types were 

 crossed together they produced an F^ of A and B plants. 



The cytological aspects of this problem were also investigated. 

 In the case of the hybrid (E. ammophila X (biennis X ruhricalyx) 

 a ring of eight chromosomes was obtained as well as three bivalents. 

 Most usually the three bivalents took the form of rings, while the 

 closed chain was much contorted and twisted to enable it to lie 

 in the nuclear cavity. At metaphase, adjacent chromosomes 

 became attached to the fibres of the spindle and the three free 

 pairs of chromosomes took up their position about the equatorial 

 region of the spindle. At anaphase the three bivalents assorted 

 in the usual way, each chromosome travelling to the opposite pole 

 of its homologue. Fairly frequent instances of non-disjunction 

 and lagging of chromosomes were observed, as well as fragmenta- 

 tion at anaphase. 



In the case of the reciprocal hybrid, CE. {biennis X rubricalyx) X 

 ammophila, a small ring consisting of a single pair of chromosomes 

 was cut off from the spireme very early as the knot from the 

 second contraction loosened out. When further unfolding of the 

 knot took place, six further rings were set free. When the bipolar 

 spindle was formed, as a rule most of the bivalents came to lie near 

 the equatorial region. They never, however, formed a regular 

 equatorial plate. Usually some of the bivalents approached the 

 centre of the spindle and the mates separated, wiiilst the other 

 homologues were still joined. This resulted, as a general rule, in 

 a very irregular metaphase and anaphase. As the metaphase was 

 so irregular, it is clear that the univalents comprising each separate 

 group of chromosomes could not travel simultaneously to the 

 opposite poles. Once the homologues broke apart they separated 

 rapidly, but the univalents which compose each daughter nucleus 

 would travel to the poles in a procession. 



In the cross CE. (biennis X rubricalyx) X ammophila at 

 diakinesis seven bivalents were always observed. It was quite 

 otherwise with the cross CE. ammophila x (biennis X rubricalyx). 

 In a few pollen mother-cells the amount of chromosome linkage 

 was found to be abnormal. In one case, four bivalents and a closed 



