LIFE HISTORY OF PINUS 29 



these segments are actually flattened out is further shown by 

 the fact that the arms which remain united and elongated stain 

 much less deeply than do those which, having become free, 

 have contracted to nearly their former length. This would 

 seem to indicate that the chromatic spireme is a plastic or viscid 

 body. Lloyd ('02) describes a similar action, though much 

 less marked, in Crticianella. While the position of the retreat- 

 ing half chromosomes is such as to give ordinarily the appear- 

 ance of V's or U's, other figures occur with sufficient frequency 

 to establish the reality of their persistence after the close of the 

 metaphase of the division. This point will be considered more 

 fully later. 



The achromatic figure increases but little in length as the 

 chromosomes pass to the poles so that the movement here must 

 be due in large measure to a pull exerted by the contracting 

 fibers and not to any great extent to a push brought about by 

 the growth of the central spindle. If the force which seems 

 necessary to effect the separation of the half chromosomes is 

 furnished by the achromatic fibers, we should expect to find the 

 poles of the spindle firmly buttressed as described by Stras- 

 burger ('00) for Larix ; but no strengthening fibers are devel- 

 oped, and, although the apices of the spindle are usually 

 inserted in the ectoplasm, they not infrequently end blindly in 

 the cytoplasm. It is possible that the force exercised by the 

 growing fibers of the central spindle just equalizes the counter 

 force exerted by the mantle fibers in drawing the chromosomes 

 to the poles, the equilibrium thus established giving rigidity and 

 rendering a support for the poles unnecessary. By the time 

 the pairs of daughter-chromosomes have reached the poles they 

 have become much reduced in size and regular in contour (figs. 

 27 and 30). 



After the chromosomes reach the point where the daughter- 

 nuclei are to arise, they do not at once fuse end to end to form 

 a continuous spireme, but as the chromosomes lie side by side 

 they lose their clear outline and gradually assume a diffuse 

 reaction to stains. In this condition the halves of the longi- 

 tudinally split pairs of chromosomes are doubtless fused, after 

 which fusion the adjacent segments unite by their ends to 



