39 



Fig. 2. 



Fig. 2. Diagrams illustrating the behavior of the chromatin during the two matura- 

 tion divisions in a spore mother cell. a~f. first or heterotypic mitosis, a. resting 

 niicleus, same as in fig. 1. h. longitudinally split chromatin spirem developed from a; 

 the halves of the spirem are twisted upon each other, c, spirem has segmented into 

 eight chromosomes which have approximated in pairs to form the four bivalent chromo- 

 somes. These eight chromosomes were united end to end in the spirem of b, just as in 

 the ordinary somatic mitosis, d. spindle with the four bivalent chromosomes arranged 

 in the equatorial plate, e. anaphase, the four chromosomes retreating towards the poles 

 of the spindle. Each of these retreating chromosomes is now more clearly seen to be 

 composed of two halves which were formed by the longitudinal splitting in b. f. daugh- 

 ter nuclei in which the spirems will be formed by the union end to end of the daughter 

 segments. This is the division in which the number of chromosomes is reduced to one- 

 half, because whole chromosomes pass to each daughter nucleus. If these whole chromo- 

 somes are different in hereditary characters, the division is qualitative or differential. 

 Q—i- second or homotypic mitosis, g. spindle showing the four chromosomes arranged 

 in the equatorial plate; the free ends of the daughter segments of each chromosome 

 diverge from each other, h. the segments passing to the poles of the spindle, i. the 

 grand-daiighter nuclei resulting from the second mitosis. This is an equasional division, 

 because it consists of the separation of half chromosomes, or daughter segments, formed 

 by the longitudinal fission of whole chromosomes. 



