210 BOTANY 



they are all linked together in a single ring. At metaphase, 

 neighbouring chromosomes become attached to the fibres of 

 different poles and are slightly drawn towards the pole to 

 which they are ultimately destined. This results in the zig-zag 

 arrangement so typical of (Enothera species in which a large 

 amount of chromosome linkage prevails. As in the reciprocal 

 hybrid, there was a marked tendency for the ring to break into a 

 single chain prior to metaiDhase. Many instances of non-disjunc- 

 tion and double non-disjunction were observed, approximately 

 10 to 11 per cent, of the former. 



CE. ammophila X novce-scotice. The F^ generation in this 

 hybrid all showed novce-scotice characters very strongly. At 

 diakinesis the hybrid was characterised by the complete absence 

 of pairing of the chromosomes, and once more in this case all the 

 chromosomes were linked together in a single long closed chain. 

 They remained in this condition till metaphase, when alternate 

 chromosomes segregated. Non-disjunction was shown in a 

 number of cases. 



(E. ammophila X rubricalyx. In this form a relatively large 

 number of the chromosomes shows pairing during diakinesis and 

 metaphase, and only six remained linked together in a ring. The 

 pairs from the small rings, as in the parental types, do on occasion 

 become interlocked with each other or with the large ring. There 

 is often a curious infolding of the nuclear membrane during 

 diakinesis. The amount of non-disjunction was about 8 per cent., 

 and double non-disjunction was also frequent. 



CE. eriensis X rubricalyx. During diakinesis and metaphase, 

 twelve of the fourteen chromosomes of the hybrid were linked 

 together to form a closed chain, while the remaining two chromo- 

 somes formed a small ring-pair. The chromosomes of the large 

 ring formed a zig-zag pattern at metaphase and adjacent ones 

 separated at anaphase, when the homologues of the small ring-pair 

 also separated. Again non-disjunction (10 per cent.) and double 

 non-disjunction was frequent. 



CE. rubricalyx x novce-scotice. In this case a ring of twelve 

 chromosomes was formed. At anaphase segregation occurred in the 

 usual way. The amount of non-disjunction was over 12 per cent. 



