VII] PLANT POPULATION 109 



a single parent would if unchecked cover an area 

 2000 times as great as the surface of the dry land in 

 the course of three years. A glance at the figures 

 quoted for Orchids, Ferns, Moulds, and Bacteria 

 shows that the Flixweed is by no means an extreme 

 case of fecundity. It is hardly possible to express in 

 words the consequences of successful establishment 

 of every germ which such plants might produce within 

 even a moderate period of time. 



There is no need to astound or stupify the mind 

 by the statement of further figures such as those 

 above quoted. No brain can realise what is meant 

 by a million units, and speaking of billions conveys 

 no more than some general impression of vastness. 

 What is desired is to make it clear that the production 

 of potential germs is very great, and that even in cases 

 of relatively low productivity the number of germs 

 produced is far in excess of the actual requirement 

 to make up directly for losses by death. There is in 

 fact an immense overplus, which may be held as a 

 very efficient reserve to meet, with an ample margin 

 to spare, all the contingencies involved in the estab- 

 lishment of the germ, and its continued existence up 

 to the time of its propagative maturity. 



But there is another circumstance to be considered 

 besides the mere number of the progeny. There is a 

 diversity in different types of plants in the time 

 required for the individual to reach the reproductive 



