26.] CHAPTER T. THE CELL. 12] 



partition of the parent cell. A further, though not absolute, 

 distinction is, that in the latter mode each nuclear division is 

 immediately followed bj a corresponding cell-division, whereas 

 in the former, no cell-division takes place until all the (or very 

 many) nuclear divisions have been completed. Finally, when the 

 cell-formation is accompanied, as it frequently is, by the develop- 

 ment of a cell- wall, the cell- wall formed in connexion with simple 

 cell-division is merely a septum in the plane of division, that is, a 

 wall which abuts upon the side- walls of the parent cell, whereas 

 in free cell-formation walls are formed all round the new cells. 



(a) Free cell- formation may take place either in a cell or in 

 a coenocyte. In the former case it is preceded by successive 

 indirect nuclear divisions the cell becoming, in fact, a ccenocyte 

 for the time being until the requisite number of nuclei are 

 formed ; in the latter case nuclear division may or may not be 

 necessary. 



The product of this process of cell-formation is either, as com- 

 monly happens, a number of free cells, with or without proper 

 cell-walls ; or, a cellular tissue. 



The formation of isolated cells occurs only in connexion with 

 the development of reproductive cells and only in certain plants : 

 e.g. the zoogonidia and gametes of cosnocytic isogamous Algae, 

 such as some Confervoideae and Siphoneae, and the Hydrodictyeae ; 

 the spermatozoids and oospheres of the coenocytic but heterogamous 

 Sphaeroplea; the zoogonidia of the Phaeosporeae, and the sperma- 

 tozoids of the Fucaceas, among cellular Algae ; among Fungi, the 

 spores and gonidia of the Mucorinae, the zoogonidia and oospheres 

 of the Saprolegniese (Fig. 79), the ascospores of the Ascomycetes 

 (Fig. 80) ; in the Phanerogams, the egg-apparatus of Angiosperms, 

 and the embryo-sporophyte of Ephedra. 



In this case the process of cell-formation is simple ; the proto- 

 plasm, under the influence of the kinoplasm, segregates round 

 the individual nuclei, constituting distinct cells which may or 

 may not develope proper walls ; the development of the walls (if 

 present) takes place in the manner already described (p. 117). 



The development of a tissue by free cell-formation is not com- 

 mon ; it occurs in the development of the endosperm of the 

 Phanerogams, in that of the female prothallium of Isoetes, and 

 in that of the embryo-sporophyte of Gingko and of the Cycads 

 (p. 15). Here, after the formation by division of the requisite 

 number of nuclei, the cytoplasm becomes marked out into units 



