12 A PRIMER OF BIOLOGY 



branches. These projections are approximately 

 alike in their early stages of development and both 

 are green ; but ere long one of them becomes swollen 

 and somewhat pear-shaped and isolated from the 

 main filament by a transverse wall. The other pro- 

 jection becomes hooklike and a partition appears 

 just where the bend occurs. The region beyond this 

 partition loses its green colour and its protoplasmic 

 contents subdivide into many extremely minute 

 ovoid particles, each of which, when examined under 

 a high power of the microscope, is seen to be provided 

 with two cilia pointing in opposite directions. When 

 these bodies, known as sperms (or antherozoids), are 

 ripe, they escape by an opening formed at the apex of 

 the curved branch. Simultaneously the short adjacent 

 projection becomes mature by the aggregation of 

 the green contents into a central mass having a colour- 

 less apical region, in front of which the wall is much 

 thinner and finally disappears, allowing part of the 

 colourless portion of the contents to escape as a 

 minute drop of mucilage. The sperms are attracted 

 by this mucilage, and one of them finds its way into 

 and fuses with the central green mass, which is known 

 as the ovum. The product of fusion, or oosperm, 

 as the result of this sexual reproduction may be 

 termed, then becomes enclosed in a wall and behaves, 

 after a period of rest, in a manner precisely similar 

 to the zoospore, i.e., it germinates into a new plant. 

 The same result is thus arrived at in both asexual and 

 sexual reproduction but in entirely different ways ; 

 in the asexual method one part only becomes the 

 " germ " of the future plant, but in the sexual 

 method the " germ " is the product of fusion of two 

 parts, one the relatively large passive ovum, the other 

 the minute motile sperm. 



