LIFE HISTORY OF PINUS 2*J 



intimate relation between nucleolar and chromatic substances. 

 Whether the nucleoli are actual reservoirs of chromatin which 

 is given out passively to the chromatic thread, or whether they 

 are actively engaged in furnishing nourishment to the chromatic 

 substance, I have not been able to determine, but, from certain 

 observations to be described in a later chapter, I am inclined to 

 consider them more than passive elements of the cell. 



Coordinate with the formation of the chromosomes the nuclear 

 membrane resolves itself into a weft of threads which crowd 

 into the nuclear cavity, together with delicate granular fibers 

 from the cytoplasm. The latter are evidently formed by a re- 

 arrangement of the granules of the cytoplasmic reticulum. Up 

 to this time the cytoplasm has remained close meshed in the 

 region of the nucleus but has become less dense at the periphery 

 of the cell. As the nuclear membrane disappears, coarser 

 reticulations arise in the cytoplasm and extend towards the 

 nucleus, doubtless contributing to the forming spindle. When 

 the achromatic figure is fully developed, the cytoplasm again 

 becomes uniform in structure throughout the cell, but there 

 seems to have been an actual loss in granular substance, the 

 meshes of the network being much larger now than formerly 

 (figs. 20 and 21). A few delicate fibers may be seen in the 

 cytoplasm just before the dissolution of the nuclear membrane, 

 but, although I have searched repeatedly for cytoplasmic phe- 

 nomena such as that described by Mottier ('97 and '98), Duggar 

 ('00), Juel ('00) and others, I have never been able to detect 

 anything at all comparable with the structures figured by these 

 authors. If they are present in Pinus, I have not been able to 

 differentiate them with any of the stains used. 



The spindle is almost invariably tripolar in origin, but it may 

 arise as a multipolar diarch. In either case, its ultimate form 

 is that of a sharply pointed bipolar spindle (Figs. 21-24). 

 Belajeff ('94) describes this spindle as many poled in origin in 

 Larix, and Mottier ('97) makes the same statement for Pinus; 

 but in the many thousands of karyokinetic figures observed for 

 this division, I have never found one that showed more than 

 three poles. A few scattering fibers have occasionally been seen 

 to pass from all sides towards the nucleus but achromatic threads 

 have not been found to converge at more than three points. 



