1908] GATES— REDUCTION IN OENOTHERA 21 



more or less intimately about the time of synapsis or later. After the 

 events of synapsis, a longitudinal split reappears in the thickened 

 spirem threads, this split representing the line of approximation of the 

 two original spirems. Transverse segmentation into pairs of chro- 

 mosomes, which are believed to be homologous somatic chromosomes 

 of maternal and paternal origin, then takes place. The halves of these 

 bivalent chromosomes, which lie side by side, are then distributed 

 in the heterotypic mitosis, which is thus a reduction division. In 

 the anaphase of the heterotypic mitosis a longitudinal split appears in 

 the daughter chromosomes, which is regarded as a premature split 

 for the homotypic mitosis, the latter being thus an equation division. 

 The persistency with which this general account has been given, not- 

 withstanding differences in detail, particularly preceding and during 

 synapsis, leads the writer to the belief that it is probably correct in its 

 main outlines, at least in many of the forms described. This being 

 judged to be the case, every effort was made to bring the account in 

 Oenothera into harmony with this general course of events but with- 

 out success, for Oenothera is found to deviate in some important 

 particulars, as is already evident from the description. 



Another general account of reduction in plants, which was adhered 

 to by Strasburger as late as 1904 (30), and has been held notably 

 by Farmer and Moore (8, 9), Farmer and Shove (10), Schaffner 

 (28) , Mottier (19, 20) , and others, to mention only a few of the recent 

 papers, is in general as follows: The split in the spirem which occurs 

 at about the time of synapsis is a true split, such as may occur in the 

 prophase of somatic mitoses, and is not preceded by a pairing of 

 parallel threads, but the thread is single from the beginning. This 

 split afterward closes up as the thread shortens and thickens after 

 synapsis, and the single spirem so formed segments usually into the 

 reduced number of chromosomes, which are thus arranged successively 

 end to end. Each such bivalent chromosome thus consists of two 

 halves arranged end to end, not side by side, and the heterotypic 

 mitosis thus separates successive whole chromosomes on the spirem, 

 being therefore, as in the other account, a reduction division. The 

 split which appears in the anaphase of this mitosis is interpreted as a 

 reappearance of the earlier longitudinal split of the spirem. The 

 homotypic mitosis is therefore an equation or longitudinal division. 



