105 



all the spores of the sporancjium, can be readily distinguished 

 from the surrounding somatic cells. It is larger, and the chroma- 

 tin of the nucleus stains much more deeply than that of the other 

 cells. The chromosomes are large and distinctly looped, and in 

 the metaphase of karyokinesis they are split by a longitudinal 

 division (Fig. 17). After each division the daughter-nuclei pass 

 into the resting stage, during which the cell-walls are com- 

 pletely formed and each daughter-cell becomes completely sepa- 

 rated. The resting stages are comparatively long and the division 

 stages short. 



I . The groivtJi-period. 



After the sixteen primary sporocytes are formed the nuclei 

 pass as usual into the resting stage (Fig. i). The nuclei are at 

 first comparatively small (10.3 //. in diameter), the chromatin-reti- 

 culum does not stain intensely, and there are usually from one to 

 three or more nucleoli in each. Meantime the tapetal cells degener- 

 ate, giving room for growth of the reproductive elements. This 

 growth must begin very soon for the cells in the resting stage 

 (Fig. i) are not frequently found. When fully grown, the nuclei 

 measure about 14.5 // in diameter, an increase of nearly 50 per 

 cent. During this enlargement the chromatin reticulum is con- 

 verted into a delicate moniliform spireme. This is a single thread 

 of chromatin, very much coiled and interwoven and at first distri- 

 buted evenly throughout the nucleus (Fig. 2). From this condi- 

 tion of extreme delicacy and expansion the chromatin soon passes 

 into a stage of greater localization and the spireme becomes 

 thicker. Evidence of the beginning of concentration can be seen 

 in Fig. 2 an early stage, where the nucleolus has not disappeared. 

 In a later stage, to which Farmer has given the name " Synapsis," 

 the meshes are drawn towards one side of the nucleus into a much 

 more compact chromatin mass (Fig. 3). This mass next becomes 

 loosened and the filaments more or less isolated. In exceptionally 

 favorable preparations the spireme in this stage is seen to be 

 double (Fig. 3 x). 



The concentration of the chromatin at the same time with the 

 thickening of the spireme seems to indicate a coalescence and 

 union of the formerly distinct granules of chromatin in the deli- 

 cate moniliform spireme. 



