204 BOTANY 



Following on the earlier work of Gates and Cleland, Sheffield 

 has published an important account of cytological studies of 

 certain of the meiotic stages of (Enothera. Five species were 

 investigated : CE. novce-scotice, CE. eriensis, CE. ammophila, (E. 

 rubricalyx and CE. Agari. 



At prophase the reticulum was found to be resolved into a 

 single apparently continuous thread which was in connection with 

 the nucleolus. The spireme thread then gradually shortened 

 and thickened, and all the loops were tightly drawn into 

 a tangled deeply staining knot, from the end of which the 

 loops sometimes projected. This knot lay close to the nucleolus. 

 CE. 7iovce-scoti(je behaved somewhat differently from this general 

 rule during the presynizetic and synizetic stages, for at early 

 synapsis large variously shaped chromatin masses made their 

 appearance (Fig. 76, 4). In CE. Agari, CE. eriensis and the hybrid 

 CE. rubricalyx x CE. ammophila these masses disappeared at an 

 early stage, being apparently reabsorbed by the thread. In 

 CE. novce-scotice these rounded chromatin masses were often found 

 to be connected into a kind of chain. They disappeared, however, 

 at pachynema. A second contraction now followed, and 

 when the bivalents emerged, it was not usual to find them 

 paired. They were generally arranged in rings, consisting 

 of varying numbers of univalents, and the number present 

 in each ring was practically constant for each species. In 

 CE. novce-scotice and CE. eriensis the chromosomes were arranged 

 in a single ring of fourteen chromosomes. In CE. ammophila there 

 was one pair of chromosomes cut off from the rest which lay in a 

 continuous ring. Four pairs were cut off in CE. rubricalyx and a 

 ring composed of six chromosomes was left. Closed rings were 

 also present in CE. Agari, but these were not found to be constant 

 in their construction. These rings of chromosomes are drawn on 

 to the spindle at metaphase. 



The formation of the large rings of chromosomes in the later 

 stages of prophase, instead of the usual pairing of bivalents, has 

 been described for many species of CEnothera. When some, or all 

 of the chromosomes are arranged in rings and at anaphase alternate 

 chromosomes pass to opposite poles of the spindle, they are not 



