36 



HEREDITY AND EVOLUTION IN PLANTS 



28. Nature and Method of Reduction.— In order 

 thoroughly to understand fertilization and reduction one 

 must have a knowledge of the structure and behavior of 

 the nucleus in cell-division and cell-fusion. This subject 

 is too difl&cult and too extended to be thoroughly treated 



Fig. 30. — Diagram illustrating various stages of indirect nuclear 

 division (mitosis). A, resting nucleus of the mother-cell; B, formation 

 of nuclear skein or spirem; C, longitudinal splitting of the spirem; D, the 

 chromosomes (four in number) have been formed by the transverse seg- 

 mentation of the spirem; E, chromosomes arranged on the equator of the 

 nuclear spindle; F and G, early and late anaphase, the chromosomes moving 

 to the pales of the spindle; H, formation of daughter spirems; I, resting 

 stage of the two daughter-cells. 



in an introductory study, but the salient facts are as 

 follows. . The nucleus of all cells comprises at least four 

 substances: nuclear sap, a threadwork of linin, and a 

 substance called chromatin;'^ all these are enclosed by a 

 nuclear membrane. In the non-dividing nucleus the 

 ' Because it stains readily when treated with certain aniline dyes. 



