30 MARGARET C. FERGUSON 



form a coiled, somewhat moniliform thread (figs. 30-32). 

 Immediately upon the formation of the skein a delicate 

 nuclear membrane appears, the coils loosen somewhat and 

 branch freely thus giving rise to a reticulum. Extensive 

 growth follows and a large " resting" nucleus is formed (figs. 

 33 and 34). The nuclear net consists at first of delicate achro- 

 matic linin threads bearing scattered chromatin-granules and 

 uniting large irregularly branched chromatic portions. Distri- 

 bution of the chromatin continues until there is a delicate linin 

 reticulum with chromatin granules of varying sizes imbedded 

 in it (figs. 33-35). These nuclei have the form of a plano- 

 convex lens the flat side of each nucleus being perpendicular 

 to the axis of the spindle and facing the other daughter-nucleus. 

 It is obvious from the foregoing that a definite resting nucleus 

 is formed in Pinus at the close of the heterotypic division. 

 This accords with the recent observations on the formation of 

 the microspore by Duggar ('99) in Bignonia, Strasburger ( 5 oi) 

 and Gager ('02) in Asclepias and Andrews ('01) in Magnolia. 

 A true nucleolus has not been observed in the daughter-nuclei. 

 Contrary to the observations of Hofmeister ('51), no cell-wall 

 is laid down and in only a very few instances has a slight 

 thickening of the spindle fibers in the region of the cell-plate 

 been observed. 



The Second Mitosis of the Mother-cell. The resting daugh- 

 ter-nuclei are scarcely more than established before the initial 

 steps of the second division are instituted, as evidenced in the 

 readjustment of the nuclear reticulum. The more delicate 

 threads of the net are withdrawn, the nuclear membrane fades 

 out, the chromatin loses its granular aspect and becomes evenly 

 distributed upon the linin, and there issues forth a heavy, homo- 

 geneous, deeply-staining band which is more or less coiled and 

 branched (fig. 36). The chromatin-thread, which now lies 

 free in the cytoplasm of the mother-cell, continues to thicken, 

 the branches or cross fibers disappear, and in an almost incredi- 

 bly short time, the delicate nuclear net has given place to a 

 broad, somewhat spirally coiled skein (fig. 37). 



Achromatic threads arise in the cytoplasm forming a multi- 

 polar diarch spindle. The fibers are not abundant and always 



