2 The Ohio Naturalist. [Vol. XIII, No. 1, 



united in pairs. He did not find a conjugation of two threads 

 during synapsis. He mentions a slight resting stage between the 

 first or heterotypic division and the second, homotypic division, 

 but does not speak of any longitudinal splitting of the hetero- 

 typic chromosomes until after the transverse splitting occurs. 

 The longitudinal splitting was visible just before the chromosomes 

 reached the poles. 



Gates (7) in his paper on Oenothera rubrinervis, states that the 

 contraction of the chromatin material is synapsis and that since 

 the cytoplasm of the cells shows no contraction, the cell is per- 

 fectly fixed. For this reason, the contraction, so constantly 

 observed at an early stage in the process, is not an artifact, but 

 is a real contraction stage, leading to synapsis. As this contrac- 

 tion proceeds the reticulm is re-arranged into a long, continuous 

 delicate thread. No indication of a doubling or pairing of the 

 threads was evident. After the synapsis the spirem shortens 

 and thickens and begins to arrange itself more loosely in the 

 nuclear cavity. This shortening is progressive and continues for 

 some time. He states that the shortening may be uniform, or it 

 may vary or may be irregularly constricted at varying intervals. 

 This thickened thread now segments transversely into fourteen 

 chromosomes — fourteen being the sporophytic number. Then 

 these chromosomes break up into pairs which later fuse with each 

 other leaving the x number of chromosomes. They are taken on 

 the spindle and reduction follows in the usual way. 



In his paper on Oenothera lata x O. gigas (9) he begins his 

 dicussion with the telophase The usual number of chromosomes 

 found in the hybrid is twenty-one, seven being of maternal and 

 fourteen of paternal origin. In the reduction one germ cell 

 receives ten and the other eleven chromosomes. In a few cases 

 nine and twelve chromosomes were the numbers found at the 

 respective poles. One cell was found which had twenty chromo- 

 somes, ten of which went to each pole. The segmentation into 

 ten and eleven proves that there is not a pairing of homologus 

 chromosomes of maternal and paternal origin but the segmenta- 

 tion tends to be into two numerically equal parts. Gates claims 

 evidence from his work, that there are two general methods of 

 chromosome reduction, one a side to side pairing of chromatin 

 threads (parasynapsis) to form a double spirem ; the other involving 

 an end to end arrangement (telosynapsis) of maternal and paternal 

 chromosomes, to form a single sjjirem which afterwards splits 

 longitudinally. He says an individual always has as many 

 chromosomes as the sum of the chromosomes in the germ cells 

 which go to form the new plant. This fact, he says, supports 

 the genetic continuity of the chromosomes. He has not shown 

 whether the chromosomes have equal or unequal hereditary 

 value. 



