Nov., 1912.] The Reduction Division in Fuchsia. g 



to be seen. As division advances the thread continues to elongate 

 up to a certain stage when it is rapidly thrown into loops (Figs. 12, 

 13, 14), and begins to shorten and thicken constantly until the 

 chromosomes are fully formed (Figs. 13, 15, 17, 21, 22). In the 

 very earliest stages of the looping (Figs. 13, 14, 15, 16) the spirem 

 may be traced for a long distance and the loops are found on the 

 upper and lower surface of the nuclear wall showing that the 

 loops are formed along the periphery of the nucleus and not as 

 loops sticking out from a synaptic knot into the nuclear cavity. 



However, in the earlier stages there is a considerable crossing 

 of threads in the center. Figure 13 shows four or more well 

 defined loops already formed. These loops and the thread of 

 which they are formed are still rather delicate. The nucleolus is 

 in the center of the nuclear cavity. In some cases the cell wall 

 begins to become somewhat indistinct at about this stage, 

 (Fig. 12), but in others the wall remains well defined until the 

 tetrads are fully formed inside the original cell. In most cases the 

 sporoc^'tes have not separated from each other nor from the 

 tapetal layer, and have in consequence, not yet rounded up. 

 The loops of the thread are formed in just such a way as loops 

 would be formed in a heavy string if two ends of the string were 

 held between the fingers and then twisted; twisting both ends in 

 opposite directions. Some of these loops showed more than one 

 twist. As the loops become tighter the spirem often appears as 

 though it contained prominent knots. The granules are still 

 very evident on the spirem where much looping has taken place 

 but at this stage no doubling was visible. This does not neces- 

 sarily indicate that division has not taken place; the granules 

 may be lying too close together to be separated with the magni- 

 fication used, or the differentiation possble with the sarfanin- 

 haemotoxylin stain. As the looping proceeds the granules 

 become less and less prominent until on the fully formed loops no 

 granules are to be seen (Figs. 15, 16, 17). The loops finally break 

 apart to form the bivalent chromosomes (Fig. 17). While chro- 

 mosome formation is going on the nuclear cavity is apparently 

 still enlarging (Figs. 15-19), but later as the nuclear wall disap- 

 pears, the cytoplasm encroaches rapidly and fills the area around 

 the contracting group of chromosomes (Figs. 20-24). Just about 

 this time the sporocytes begin to separate from each other and 

 assume a more rounded shape and the nuclear wall becomes 

 more delicate. When all the loops are fonned they lie around the 

 periphery of the nucleus and can readily be seen and counted by 

 focusing up and down. In each case the drawings were made 

 from cells whose complete nucleus showed and had been undis- 

 turbed in the cutting. It was somewhat difficult to draw correctly 

 those loops which were to the side of the nucleus where it was 

 often impossible to see the actual shape. ^ In some cases the ends 



