214 MINUTE ANATOMY OF FLO^'ERING PLANTS 



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

 tion, dragging with it the nuclens. ^ 



497. The term protoplasm includes all the living constit- 

 uents of the cell. " The word jjrotoplasm 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 bodj^ the nuclexis (Figs. 359, 862, »i), in 



many young cells occupying a 

 considerable portion of the cell 

 space; and the general mass, 

 aside from the nucleus, called 

 the cytojjlaism. 



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 

 body. 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), by 

 which equal shares in all the essential constituents of the 



361. Nuclear and cell division : 

 A^ B, C, successive stages ; 

 n, region of the nucleus; 

 c, cytoplasm : /7, d, be;,dn- 

 nings of daughter nuclei. 

 In C, the original cell has 

 become divided internally 

 into t\^"o, each Avith a large 

 nucleus in), 



— GUIGXARD. 



1 Stamen hairs of Trade scMntia, cells of the leaf of Elodea canadensis 

 or of VaUisneria spiralis, and cells of Stonewort (Chara), are objects in 

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

 Strasburger, p. 2i4. 



2 0. Ilertwig, "The Cell," p. 13. 



