g6 HEREDITY AND EVOLUTION IN PLANTS 



insects. If turf which has long been mown, and the case 

 would be the same with turf closely browsed by quadru- 

 peds, be let to grow, the more vigorous plants gradually 

 kill the less vigorous, though fully grown plants; thus out 

 of 20 species growing on a little plot of mown turf (3 feet 

 by 4) nine species perished, from the other species being 

 allowed to grow up freely." 



"Struggle for Existence" Used in a Large Sense. — "I 

 should premise," said Darwin, "that I use this term in a 

 large and metaphorical sense including dependence of one 

 being on another, and including (which is more important) 

 not only the life of the individual, but success in leaving 

 progeny. Two canine animals, in a time of dearth, may 

 be truly said to struggle with each other which shall get 

 food and live. But a plant on the edge of a desert is said 

 to struggle for life against the drought, though more 

 properly it should be said to be dependent on the moisture. 

 A plant which annually produces a thousand seeds, of 

 which only one on an average comes to maturity, may be 

 more truly said to struggle with the plants of the same and 

 other kinds which already clothe the ground. The mistle- 

 toe is dependent on the apple and a few other trees, ^ but 

 can only in a far-fetched sense be said to struggle with 

 these trees, for, if too many of these parasites grow on the 

 same tree, it languishes and dies. But several seedling 

 mistletoes, growing close together on the same branch, may 

 jTiore truly be said to struggle with each other. As the 

 mistletoe is disseminated by birds, its existence depends 

 on them ; and it may metamorphically be said 'to struggle 

 1 In the above quotation, Darwin is undoubtedly referring to the 

 European mistletoe {Viscum album). The American mistletoe (Phora- 

 dendron flavescens) is found in the eastern and central United States on 

 various deriduous-leaved trees, including the sour gum and red maple. 



