CONFERVOIDEsE HETEROGAM^E 



225 



formed at the side, through which the colourless portion of the proto- 

 plasm protrudes in the form of a papilla which takes up the antherozoids. 

 In other cases the oogone splits in the same way as the zoosporanges, 

 throwing back a kind of lid ; through the lateral crevice exudes some 

 colourless mucilage in the form of a beak-like canal, through which 

 the antherozoids enter, and coalesce with the hyaline portion of the 

 oosphere. Immediately after impregnation the oospenn invests itself 

 with a cell-wall, and assumes a "brown colour, still remaining within the 

 oogone, which separates from the other cells of the filament, and falls 

 to the ground, where the oosperm passes a period of rest before germi- 

 nation as a hypnosperm. 



FIG. 202. Bnlbochcetc setigera Ag. B, unicellular amheridial plant. A, C, young bicellular plants. 

 D, mature plant with oogone, o, and ' dwarf male,' dm (x 400). (After Cooke.) 



In some species the mode of fertilisation is more complicated. 

 Peculiar zoospores known as androspores are produced non-sexually in 

 special cells of the parent-plant, similar to those which give birth to the 

 antherozoids, only that there is in their case no preliminary formation 

 of 'special mother-cells.' These androspores, which closely resemble the 

 antherozoids in form and size, . fix themselves after swarming to a 

 definite spot on the female plant, on or near an oogone, producing very 

 small male plants, which are known as ' dwarf males ' or micrandres. 

 Each of these consists of two or three cells, the uppermost of which is 

 an antherid. This gives birth to one or more antherozoids, which escape 



