1909] SCHAFFNER— REDUCTION DIVISION IN AGAVE 205 



The spindle and late stages of synizesis. — The incept of the spindle 

 is laid down immediately over the surface of the nuclear membrane 

 while that structure is disappearing. At the same time, connecting 



promi 



? 



forming a sort of network between the chromosomes (figs. 37, 38). 

 The incipient spindle appears as a dense wall of material that was at 

 first mistaken for the modified nuclear membrane, which, however, 

 lies on the inside. This double layer about the nucleus, together 

 with the connecting strands between the chromosomes, makes an ideal 

 arrangement for abnormal contractions, and at this stage there is 

 present a final prominent synizesis of the chromosomes, together with 

 the dissolving nuclear membrane inclosing them. The chromosomes 

 at this stage have not yet fused with the surrounding spindle. A few 

 examples of this appearance are shown in figs. 32-38, all about in the 

 same stage of division. Those which show the connecting fibers less 

 distinctly are from the lighter-stained preparations. In fact, without 

 a heavy stain, the connecting threads are barely visible. The con- 

 tracted nuclei are seen in slides side by side with cells having a normal 

 appearance. There is no doubt in the writer's mind that the phenom- 

 enon is an artifact. 



pindle 



character, the fiber 



The incipient spindle soon begins to show a fibrous 

 ers at first being few and indistinct, and running 



ifi 



more or less parallel toward opposite poles ui mc «*«*~~ v -o *,. 



In many cases two more or less pointed caps extend from opposite 

 sides of the nucleus and become prominent before the longitudinal 

 nbers are visible (figs. 40-42) . The points sometimes show delicate 

 asters, as in figs. 41, 42. The spindle fibers develop rapidly, and soon 

 an oval slightly pointed structure is produced, in which the chromo- 

 somes and one or more nucleoli lie scattered about (fig. 43)- The 



eonnectin 



— ^5 nucis, are also prominent, giving me sspmuiv, ■— — o 

 a PPearance. The spindle is bipolar from the beginning, originating 

 " nd doping in the same way as in the vegetative divisions. 

 LLLMER in 1899 showed that in Hemerocallis the spindle originates 

 15 a bipolar structure surrounded bv a dark zone. This zone was 

 **rly absent in Agave, but the difference may be due to staining. 

 . ULl mer showed, however, that the incipient spindle is entirely 

 ,nsid * of the dark zone. 



