20 



PROTOPLASM 



wormlike bodies (Fig. 12) which are clearly visible only during 

 cell division. The nucleus of a "resting" cell (the term is a 

 misnomer, as the so-called "resting" cell may be very active in 

 other ways) is frequently devoid of evident structure (the resting 

 animal nucleus is usually optically empty, but the plant nucleus 

 most often reveals structure). When cells are about to divide 

 and produce two daughter cells, a marked change takes place. 

 The chromatin material (Fig. 12a) of the nucleus collects into a 

 long thread called the spireme (Fig. 126) which breaks up into 



Fig. 11. — Calcium oxalate crystal in a plant cell. (The lamellated structures at 



the periphery are starch grains.) 



segments. These segments are the chromosomes (Fig. 12c). 

 They collect at the center of the cell where they form the equa- 

 torial plate (Fig. 12d, 10c). While at the equatorial plate the 

 chromosomes are connected by spindle fibers to the poles of the 

 cell (Fig. 12c?). The fibers are still visible at a later stage (Fig. 

 12/). At a time which is not precisely known in all cases, the 

 chromosomes split longitudinally. Half of each chromosome 

 then moves (Figs. 12c, lOd) or is moved to one end of the cell. 

 Thus does each new daughter cell get part of each of the original 

 chromosomes. At their respective poles in the mother cell, the 

 newly formed daughter chromosomes collect, lose their identity 

 as distinct structures, and fuse to form the nuclei of the two 



