124 



PART IT. THE INTIMATE STRUCTURE OF PLANTS. 



[26. 



for instance, the zoogonidia and gametes of some isogamous 

 Volvocaceae (e.g. Pandorina), and Confervoidea3 (e.g. Ulothrix), 

 the spermatozoids of Volvox, the oospheres of Fucns. The pro- 

 cess is a simple one, consisting in the indirect division of the 

 nucleus, followed by a corresponding division of the cytoplasm, 

 no septum being formed. Commonly this process occurs but 

 once, two cells being formed in the mother-cell ; or it may be 



FIG. 82. Cell-division m> etaminal 1 hair of Tradescantia vvrginica (x 540: after Stras- 

 burger). 1-6 Mitotic division of nucleus; 7-11 development of the septum in the kino- 

 plasmic spindle. 



repeated twice, giving rise to four cells ; or thrice, giving rise 

 to eight cells (e.g. oospheres of Fucus) ; or many times, giving 

 rise to a large number of cells (e.g. spermatozoids of Volvox). 



The typical case of cell-division is that which is attended by 

 the formation of septa, resulting in the development of cells 

 which remain coherent to form a tissue. The process begins with 

 indirect division of the nucleus (Fig. 82, 1-6) ; when this is com- 



