40 



European thistles on the La Plata. 

 Cotton weed in the tropics. 

 White clover in New Zealand. 

 Other plants in New Zealand. 

 Lantana in Ceylon. 



The lack of increase ordinarily, in spite of the number 

 of young produced, shows that there must be a 

 large death rate. 



The checks on population and the struggle for exis- 

 tence. 



a. The scarcity of food. 



The struggle for food between individuals of the 

 same species. 



Between different species. 



Examples — The trees in a forest. 



Darwin's experiment with the turf. 



The beech and birch in Denmark. 



The water cress and the willows. 



b. Enemies. 



Dependence of herbivorous animals upon plants 

 and of carnivorous animals upon herbivorous 

 ones. 



The struggle to escape being eaten. 



Seeds. 



Absence of trees on the Pampas. 



The struggle on the river banks. 



Darwin's example of the game animals. 



P^ishcs. 



Parasites. 



