12 BOTANICAL GAZETTE [july 



Tradescantia, though he formerly thought it resulted from bad fixa- 

 tion ; and it appears to have been observed also by Farmer and Shove 

 (io). Mottier states that in these forms there is but little shorten- 

 ing of the spirem between synapsis and segmentation into chromo- 

 somes. In Oenothera, on the contrary, as is evident from a 

 comparison of figs. 15 or 16 with 22, a very considerable amount of 

 shortening as well as thickening of the spirem takes place during this 

 interval. During the second contraction the paired threads apparently 

 fuse, and further shortening of the (from now single) thread results in 

 an enormous amount of thickening of the spirem, so that when it uncoils 

 from this second contraction it has approximately the thickness of a 

 chromosome and exhibits only a few loops. It can then frequently 

 be traced through nearly its whole length. At this time there is a 

 great amount of variation in the thickness of different parts of the 

 spirem, as seen in figs. 22 and 23. Fig. 19 is a portion of the spirem 

 at this period, drawn with a higher magnification. It shows the 

 chromatic bodies, which vary in size, imbedded in the linin substra- 

 tum. As to how far two different substances are represented, I am 

 at present unprepared to say. 



DIAKINESIS 



The single thick thread now segments transversely into 14 chromo- 

 somes, the sporophyte or 2X number. At this time there is no indica- 

 tion whatever of a longitudinal split in the thread. Even when greatly 

 washed out, the material of the chromosomes appears perfectly 

 homogeneous, or if a granular structure is observable there is in its 

 arrangement no indication of the previous split. At the time of this 

 second contraction a pair of chromosomes is frequently observed 

 separated from the spirem and apparently always lying with their 

 long axes parallel and connected at one end (figs. 20, 22). This 

 condition occurs very commonly, although in other cases the spirem 

 is continuous throughout (fig. 21). In no case has more than one 

 pair of chromosomes been observed to be thus precociously cut off in 

 O. rubrinervis, though two such pairs have been observed in O. lata 

 (see 11 , fig. 19) . In no case has a single chromosome been observed 

 to be cut off in this manner, and apparently they are invariably cut 

 off in pairs, that is, bivalvent chromosomes are detached. 



