THE ALG.E 



209 



crowded branches of the bushy stem), where its future 



development is most secure. In such a position, 



however, it is not readily accessible to the male cells, 



and consequently we always find 



in connection with it the hair-like 



trichogyne, which projects far out 



towards the exterior, and thus 



reaches the exposed part of the 



thallus to which the spermatia 



are likely to be conveyed by the 



chance currents of the surrounding 



water. 



When a spermatium happens 

 to reach the trichogyne it adheres 

 to its gelatinous cell- wall, and is 

 thus held fast (see Fig. 90, s). 

 In the mean time the spermatium 

 has formed a membrane round its 

 protoplasm. At the point of 

 contact between spermatium and 

 trichogyne the cell - walls are 

 absorbed, and so the contents of 

 the male cell are enabled to enter 

 the receptive organ. All the 

 parts concerned are very minute, 

 but the details of fertilisation have 

 now been completely followed in 

 certain instances. This was first 

 accomplished in Nemalion, a genus 

 rather simpler in its arrangements 

 than our type. The nucleus of 

 the spermatium travels down the 

 trichogyne and fuses with that of 

 14 



Fia. 90. Callithamnion 

 corymbosum ; part of a 

 branch of a female plant, 

 bearing a procarpium. 

 t, apex of the long 

 trichogyne; s, a sperm- 

 atium adhering to it ; a, 

 carpogonium, at base of 

 trichogyne just below 

 this is one cell of the 

 trichophore ; c, the other 

 trichophore cell. The 

 two cells showing to the 

 extreme right and left 

 of the trichophore are 

 the auxiliary cells, which 

 fuse with the carpogon- 

 ium. Magnified 250. 

 (After Thuret and 

 Bornet.) 



