LIFE HISTORY OF PINUS 73 



greater magnification, be resolved into slightly irregular and 

 roughened bodies, as in the prophase of the heterotypical mitosis 

 in the microspore-mother-cells, but with the powers of the micro- 

 scope at my command, I have no evidence that such is the case. 



The phenomenon of synapsis is as marked here as in the 

 primary mitosis of the microspore-mother-cell, but the contracted 

 mass is less dense, probably because of the smaller size of the 

 nucleus and the consequent diminution in nuclear substance 

 (fig. 127, plate XIII). With the recovery from synapsis the linin 

 thread is seen to have increased in thickness, and the chromatin- 

 granules are irregularly distributed upon the continuous spireme, 

 which gradually comes to fill the entire nuclear cavity with 

 its open uninterrupted coils (figs. 128 and 129). The chro- 

 matic substance again collects into definite areas of varying 

 dimensions, which are united by clear portions of the linin- 

 band, and the longitudinal splitting now becomes apparent. 

 Condensation and segmentation follow, and the distinct chro- 

 mosomes, in the reduced number, become evident (figs. 130, 

 132 and 133). The forms of the chromosomes are similar to 

 those already described in connection with the division of the 

 microspore-mother-cell (figs. 132-136). Because of the com- 

 paratively small size of these nuclei, the steps by which the 

 irregularly shaped chromosomes are derived could not be traced 

 with the same degree of confidence as in the microspore-mother- 

 cell ; but the entire phenomenon is such as to indicate very con- 

 clusively that the process is practically the same in both. 



The spindle, at first a multipolar diarch, early becomes bi- 

 polar and during metakinesis it is very sharply so. The poles 

 do not reach the walls of the cell, but a few threads sometimes 

 radiate from them and extend to the ectoplasm. There may 

 be a slight granular condensation in the neighborhood of the 

 poles but it is never prominent and often does not appear at all. 

 The chromatic segments become short and broad at the equa- 

 torial plate, and their separation into daughter-chromosomes 

 presents the figure characteristic of the heterotypic division. 

 Unsplit ends of the chromosomes extend outward in the plane 

 of the equatorial plate, thus giving rise to dark clumps of chro- 

 matic substance along the median line (figs. 134-137). The 



Proc. Wash. Acad. Sci., July, 1904. 



