228 PLANT LIFE 



same time the chromatin increases in quan- 

 tity. Stains of various kinds show that the 

 chromatin -containing strands are, as it 

 were, becoming individualised within the nu- 

 cleus, although anastomoses between adjacent 

 strands are still of common occurrence. As 

 the strands continue to differentiate, the 

 chromatin is seen to form two parallel streaks 

 in the convoluted linin bands, but this duplex 

 appearance becomes temporarily obscured, 

 though not obliterated, at a somewhat later 

 stage. Each one of these duplex chromatin- 

 containing linin bodies is ^chromosome (Fig. 26). 

 When fully formed, the chromosomes assume 

 the form of rods, hooks, etc. The most strik- 

 ing point about the chromosomes lies in 

 the fact that their number is normally quite 

 constant for a particular species of plant. 



The chromosomes become clustered in a 

 very characteristic position, and form a zone 

 or plate across the centre of the nucleus ; but 

 preceding this arrangement, and intimately 

 connected with it, a remarkable spindle-shaped 

 structure arises in the extra-nuclear proto- 

 plasm (cytoplasm). It is made up of fibres 

 which are ultimately arranged in very much 

 the same curves as iron filings take up when 

 scattered on a piece of paper under which lie 

 the poles of a horseshoe magnet. The spindle- 

 like structure extends across the space origin- 

 ally occupied by the nucleus, while the wall 

 of the latter usually (but not always) dis- 

 appears, and the only nuclear structure that 



