Darling: Sex in dioecious plants 189 



not be accurately determined, but in side views there appeared no 

 irregularity in the figure which might indicate an unequal dis- 

 tribution ; it seems probable that each chromosome divides so 

 that each of the four daughter nuclei receives the same number. 



As the nuclear membrane begins to be formed for each 

 daughter nucleus, several masses of chromatin are visible in each; 

 and as fusion of these masses continues it is found that the two 

 daughter nuclei derived from one of the nuclei contain one more 

 chromatin mass than do the other two (figs. 34, 35). No cell 

 walls are formed until after the second division is completed ; this 

 enables one to identify with certainty the two nuclei derived from 

 the same mother nucleus. Although a less number of nuclei 

 was observed in this stage than in the reconstruction of the 

 daughter nuclei after the first division, this phenomenon of the 

 extra chromatin mass appears to be even more constant in the 

 reconstruction after the second divsion. 



+ 



As to the significance of this difference in the behavior of the 

 chromatin in the two sets of daughter nuclei, we can only conjec- 

 ture. The fact that it commonly occurs in the first division and 

 that the two daughter nuclei hand on these respective characters 

 to the nuclei derived from them, leads us to suspect that this dif- 

 ference in behavior of the chromatin is in some way connected with 

 an essential difference in its character. 



Ultimately the second chromatin body fuses with the larger 

 one, so that in the complete resting stage all four nuclei have the 

 same appearance (fig. ^6), resembling the resting stage of the 

 mother-cell nucleus. The four pollen spores are formed by the 

 simultaneous division of the cytoplasm into four parts, each con- 

 taining a nucleus. 



SUiMMARY OF OBSERVATIONS 



A. All 



nucleolus in the resting stage. The nucleolus may not be entirely 

 chromatin, since at the time of division fragments of it are thrown 

 out into the cytoplasm, where they gradually disappear. 



B. The spireme is built up by the chromatin coming out of the 

 nucleolus in the form of several spherical bodies, which may vary 

 somewhat in size ; these become attached to the linin and diffuse 

 out upon it. Usually all of these bodies appear before synapsis. 



