1908] GATES— REDUCTION IN OENOTHERA n 



POST-SYNAPTIC STAGES 



Synapsis lasts for a comparatively long time, as shown by the fre- 

 quency of its occurrence in the material sectioned. During this time 

 the spirem shortens and thickens and then begins to arrange itself 

 more loosely in the nuclear cavity. This shortening and thickening 

 is progressive (figs. 16-18) and apparently continues for some time. 

 During these stages the thickness of the spirem may be nearly uniform 

 throughout, or it may vary greatly, giving a moniliform appearance, or 

 the spirem may appear irregularly constricted at varying intervals. 

 In other cases, with a certain depth of stain it is seen to be composed 

 of lighter and darker areas more or less regularly alternating. Por- 

 tions of the thread may appear homogeneous or may show the lighter 

 and darker areas, according to the depth of stain (fig. 17). In more 

 deeply stained nuclei, such as fig. 16, the thread appears homogeneous 

 throughout. These darker areas are the chromatin discs or chromo- 

 meres of various authors; and they give the thread a very character- 

 istic appearance. During this well-defined stage the greatly thickened 

 spirem is loosely distributed in the nuclear cavity. Deeply staining 

 bodies still appear attached to or enmeshed in the coils of the thread. 

 At this time one finds undoubted indications of parallel threads. 

 When represented by camera drawings in one plane the evidence for 

 this is not so satisfactory as in the original preparation, but there is no 

 doubt of their occurrence. As already stated, in the earlier stages 

 previous to and during synapsis, parallel threads could not be observed, 

 and it has not been determined whether they were really absent or 

 whether the failure to observe them was due to their extreme delicacy. 

 Hence it cannot now be stated whether they have arisen through an 

 approximation of spirems at an earlier period, or through a split in the 

 single continuous spirem. This matter will be discussed later. 



Following this stage a second well-marked contraction takes place 

 (figs. 18, 20, 21), apparently quite as typical and constant in its occur- 

 rence as the first contraction stage, which is ordinarily identified as 

 synapsis. This contraction is of much shorter duration, however, 

 and entirely different in appearance, owing to changes which the 

 thread has undergone since synapsis, resulting in a great amount of 

 shortening and thickening of the spirem. Mottier (20) has recog- 

 nized this second contraction stage in Podophyllum, Lilium, and 



