FUNDAMENTAL PRINCIPLES 



37 



chroma tin is distributed on the linin threads in the 

 form of minute granules (Fig. 30.) At one of the stages 

 preliminary to nuclear division the linin network, with the 

 chromatin, becomes transformed into a thickened skein, 



FIG. 31. Diagram illustrating various stages in the reduction division 

 (maiosis) of a spore-mother-cell of a plant; A, resting stage of the mother- 

 cell-nucleus; B, the nuclear skein or spirem, in synizesis (during synapsis); 

 C, the spirem after synapsis, showing its double (diploid) nature; the dot- 

 ted line indicates the segmentation of the spirem into two diploid chromo- 

 somes, each of which has split longitudinally in D; E, the diploid chromo- 

 somes on the equator of the spindle of the first (heterotypic) division; 

 F, late anaphase; G, metaphase of the second or homotypic division; H, 

 late anaphase of same, two haploid chromosomes approaching the poles 

 of each spindle; 7, the four daughter-cells (spores) of the tetrad. 



which shortly becomes split into two, throughout its entire 

 length. The skein finally becomes divided transversely 

 into a number of double chromatin bodies or chromosomes. 

 The number of these chromosomes is characteristic, and 

 always the same for each species of plant. The nuclear 



