228 PART III. THE CLASSIFICATION OF PLANTS. 



by the special name spermatia. The spermatia of the Florideas 

 surround themselves with a proper wall at the time of fertilisa- 

 tion. 



The sexual organs. In those Algae in which the sexual cells are 

 similar, and the sexual process is isogamous, the sexual organs are 

 gametangia. In many cases they are unicellular and undift'eren- 

 tiated : thus, when the gametophyte is unicellular (e.g. Desmidiese, 

 Diatomacese) the cell itself constitutes the gametangium ; and in 

 some multicellular or coenocytic forms (e.g. Zygnemese, Hydrodic- 

 tyon, Confervoideae) the gametangia are simply ordinary vegetative 

 cells or ccenocytes. In some isogamous Algae, however, the game- 

 tangia are differentiated as lateral appendages, and are multi- 

 cellular, as in the Phaeosporeae ; in Cutleria it is even possible to 

 distinguish the male from the female gametangium. 



When the gametangium is unicellular or coenocytic, it usually 

 gives rise to a number of gametes; but in the Conjugate a single 

 gamete is formed. When the gametangium is multicellular, each 

 cell usually grives rise to a single gamete ; but in the male game- 

 tangium of Cutleria 2-8 gametes are developed in each cell. 



The female organ, the oogonium, is in all cases unicellular or a 

 ccenocyte ; in Sphseroplea it is undifferentiated, retaining the form 

 of a vegetative segment of the incompletely septate plant ; in 

 most cases it is more or less spherical in form, and in some species 

 of Coleochaete it is prolonged at the apex into a delicate tube, the 

 trichogyne. It opens, in most cases, by the absorption of the wall, 

 at a point opposite the receptive spot of the oosphere when that 

 is present ; but in others (e.g. Volvox, Chara) it remains closed. 

 In the former case the spermatozoid enters by the aperture ; in 

 the latter, it bores its way through the wall of the oogonium which 

 becomes mucilaginous at its exposed surface. The oogonium of 

 the Fucacese, Dictyotaceae, and Tilopteridaceae, ruptures and sets 

 free the contained female cell or cells. Usually a single female 

 cell (oosphere) is formed in an oogonium, by the rejuvenescence 

 of its protoplasmic contents ; but in various Fucaceae, the proto- 

 plasm divides to form two, four, or eight oospheres, and in the 

 coenocytic oogonium of Sphaeroplea there are several oospheres. 



The female organ of the Rhodophyceae, the procarp, is some- 

 times unicellular (e.g. Nemalieae), but more commonly multi- 

 cellular. It is in nearly all cases prolonged into a trichogyne, the 

 basal portion being termed the carpogonium. The trichogyne re- 

 mains closed. The protoplasm of the procarp does not undergo 



