214 MINUTE ANATOMY OF FLOWERING PLANTS 



directly in contact with the walls, may be in slow rota- 

 tion, dragging with it the nucleus. ^ 



497. The term protoplasm includes all the living constit- 

 uents of the cell. " The word protoplasm is a morpho- 

 logical term. . . . Protoplasm is not a single chemical 

 substance, however complex in composition, but is com- 

 posed of a large number of different chemical substances, 

 which we have to picture to ourselves as most minute 

 particles, united together to form a wonderfully complex 

 structure. ... In this mixture of substances, the wonder- 

 ful vital phenomena may very frequently be observed 

 (contractility, irritability, etc.)." ^ 



Of the protoplasmic cell contents we have to distinguish 

 a rounded central body, the nucleus (Figs. 359, 362, n), in 



many young cells occupying a 

 considerable portion of the cell 

 space ; and the general mass, 

 aside from the nucleus, called 

 the cytojylasm. 



The nucleus is denser than 

 the cytoplasm. It is made up 

 of definite parts, differing in 

 chemical constitution, definitely 

 arranged. Although actually 

 of extremely small size, the nu- 

 cleus is a highly organized 

 bod}'. It is the controlling part 

 of the cell. It is the first part 

 to divide when new cells are to 

 be formed, and in division 

 passes through a complicated 

 series of changes (Fig. 361), b}^ 

 which equal shares in all the essential constituents of tlie 



361 



Nuclear and cell division : 

 A,B,C, successive stages ; 

 n, region of the nucleus ; 

 c, cytoplasm ; d, d, begin- 

 nings of daughter nuclei. 

 In C, the original cell has 

 become divided internally 

 into two, each with a large 

 nucleus (n). 



— GUIGNARD. 



1 Stamen hairs of Tradescantia, cells of the leaf of Elodea canadensis 

 or of Vallisneria spiralis, and cells of Stonev^ort (Chairt), are objects in 

 which movements of protoplasm may be studied. See Goodale, Ch. VI. ; 

 Strasburger, p. 244. 



20. Hertwig, "The Cell," p. 13. 



