CHAP, iv.] REPRODUCTION OF PLANTS. 119 



general evolution of sexual reproduction, one change has 

 been from that primitive condition where the two ele- 

 ments male and female are both motile, or possessed 

 of voluntary movement, to the condition attained by all 

 Phanerogams, where both are passive or motionless, and 

 in numerous instances their union, as will be explained 

 in detail, is effected by modifications of the plant that 

 enable it to utilize external agents for this purpose, as 

 the wind, or even members of the Animal Kingdom, 

 mostly insects. 



A marked differentiation of sexes has been reached in 

 the common large olive-brown seaweeds included under 

 the generic name of Facus (Fig. 27), where the proto- 

 plasm of the female cell becomes divided into four or 

 eight portions depending on the kind examined ; when 

 ready for fertilization the wall of the cell splits, and the 

 separate portions of protoplasm each a cell without a 

 cell- wall escape into the water, but are entirely devoid 

 of voluntary movement ; at the same time the protoplasm 

 of the male cells divides into a large number of minute 

 cells, each furnished with cilia and without a cell- wall ; 

 these cells, called anther ozoids, escape into the water and 

 swim about until they come in contact with a passive 

 oosphere, fertilization being effected by the blending of 

 the two bodies. In Fucus, then, the point has been 

 reached where the female organ is passive or motionless ; 

 but the peculiarity of this batch of plants consists in the 

 female portion or oosphere escaping from the parent 

 plant before fertilization, a weak point, not to say a 

 decided mistake, and terminating abruptly with the 

 small batch of seaweeds where it originated, the weak 

 point consisting in the absolute necessity on the part of 



