82 PART I. THE MORPHOLOGY OF PLANTS. [ 17. 



lower it is the rule that the male gametes are produced several 

 together from one mother-cell. The female gametes are de- 

 veloped singly in the mother-cell, except in the Saprolegniacese 

 among Fun^i, and in some genera of Fucacese (Pelvetia, Ozothal- 

 lia or Ascophyllum, Fucus), in which from two to eight (Fucacese) 

 or up to twenty (Saprolegniaceae) oospheres are produced from one 

 mother- cell. 



With regard to the development of the gametes, it is sometimes 

 the case that the whole of the protoplasm of the mother-cell is 

 used in their formation. Thus, the gamete of Spirogyra is formed 

 by the rejuvenescence of the whole protoplasm of a cell of the 

 filament ; and the oospheres of Fucus are formed by the division 

 of the whole of the protoplasm of the mother-cell. But in most 

 cases a portion of the protoplasm, and more particularly of the 

 nuclear substance, is excluded from taking part in the formation 

 of the gametes : a portion of it is either directly cut off by 

 division, or is simply not used in the development of the gamete. 

 Thus, in the Bryophyta, Pteridophyta, and Gymnosperms, the 

 development of the oosphere begins with the division of the 

 nucleus of the mother-cell (central cell) into two ; this is followed 

 by the division of the mother-cell into two unequal parts, no 

 cell- wall being however formed ; the larger portion is the oosphere; 

 the smaller, which eventually decomposes, is termed the ventral 

 canal-cell, on account of its position in the female organ. In cer- 

 tain Algee the development of the oosphere is attended by (e.g. 

 Yaucheria, GEdogonium, Coleochsete) the discharge of a mass of 

 protoplasm from the female organ prior to fertilisation, which 

 probably corresponds to the ventral canal-cell of the higher 

 plants. 



With regard to the development of the spermatozoid, it ap- 

 pears, in those cases in which it has been most fully investigated 

 (Bryophyta, Pteridophyta), that only a portion of the cytoplasm 

 and nuclear substance of the mother-cell is used in its formation ; 

 the residue is usually discharged with the spermatozoid, as a vesi- 

 cle which adheres to it, until thrown off by its active movements. 

 (For details, see Part II., Cell- Formation, p. 116.) 



The masses of protoplasm which are derived from the mother- 

 cells, but are excluded in any of the above ways from entering 

 into the formation of the gametes, are termed, generally, polar 

 bodies. Their physiological significance is considered in Part 

 IV. (p. 772). 



