162 REPRODUCTION 



cells. These spores, in fact, enable the plant to "carry on" 

 when the ordinary yeast cell would die for want of moisture 

 and food. Many other fungi reproduce by means of spores. 

 The filament of a mould, for instance, may undergo a series 

 of constrictions and come to look like a string of beads. The 

 beads break off one by one and each forms a spore. In other 

 species a number of spores will, be formed inside the cellulose 

 cell-wall of the filament. These are termed endospores, and 

 when released they have similar powers of resisting adverse 

 circumstances, and they help to spread the plant by being 

 blown about. 



Many algae and some fungi that live in damp places pro- 

 duce spores which swim actively through the water by the 

 aid of one or two flagella. These are motile zoospores. 



Vegetative Reproduction 



There is, however, another method of reproduction which 

 occurs in most plants and in many of the lower animals. 

 Parts of the body may separate off from the main organism 

 and grow into complete individuals. 



When a plant reproduces itself by simply separating off a 

 part of its body, the process is called vegetative reproduction. 

 For a time the body w^hich is going to form the new in- 

 dividual is attached to its parent and nourished by it; but 

 after a time it separates off and becomes an independent 

 organism. 



Now plants produced in this way are part of their parent. 

 These reproduce all the characteristics of the parent. They 

 show no variations such as are introduced when fertilization, 

 i.e. the union of two cells, gametes, each from a different plant, 

 takes place. Vegetative reproduction is very common amongst 

 higher plants. 



A Canadian water- weed known as Elodea was introduced into 

 the river Cam about 75 years ago by a Professor of Botany at 

 Cambridge whose name it is kindlier to conceal, but the plant 

 was locally known as Bahingtonia ahominahilis. It grew to such 

 an extent that it spread through all our streams and canals 

 and at times choked them. As only the female plant was intro- 

 duced and not the male, the whole of this extraordinary 



