152 STRUCTURAL BOTANY 



light more than before, and its movements are then 

 directed towards the bottom of the water or solid objects 

 contained in it ; at last it comes to rest, and in doing so 

 attaches itself by its pointed end to some solid body. 

 It loses its cilia, and now for the first time forms a cell- 

 wall of its own. The free end grows out, divides by a 

 transverse wall, and thus starts a new (Edogonium filament, 

 like that from which it was produced. This mode of 

 reproduction by actively-moving spores, capable of 

 immediate germination, is extremely common among the 

 Algae. It is characteristic of most of the pure-green 

 group, whether inhabitants of fresh water or of the sea, 

 and extends also to certain other families. 



b. Sexual 



(Edogonium is propagated very freely by the simple 

 method just described, but it also possesses a mode of 

 sexual reproduction essentially similar to that of the 

 higher Cryptogams, in so far as it consists in the fertilisa- 

 tion of a relatively large and stationary ovum by a small 

 and actively-moving spermatozoid. The distribution of 

 the sexes varies much in the different species of the 

 genus. Some are monoecious, others dioecious, while in 

 a third set (the most numerous) a more complex arrange- 

 ment prevails. In monoecious species, the male organs 

 are formed by successive transverse divisions of one of 

 the thallus-cells, the divisions all taking place near the 

 upper end of the mother-cell, so that a row of rather 

 flat cells is produced. These may divide again further, 

 producing a chain of about a dozen cells in some cases, 

 each of which is an antheridium. In every antheridium 

 the contents divide into two, and each mass becomes a 

 spermatozoid. The spermatozoids resemble the zoospores, 



