XIV.] 



A SPECIFIC EXAMPLE. 



259 



of sixty -eight, 

 follows : 



The censuses at the three dates were as 



Crab grass {Panicum sanguinale) . 

 Black Medick {Medicago lupulina) 



Purslane 



White Clover 



Eed Clover 



Red-root {Amarantus retroflexus) . 

 Ragweed {Ambrosia artemiscefolia) 

 Pigeon -grass {Setaria glauca) . . 

 Pigweed {Chenopodium album) . . 

 Shepherd's Purse 



July 10 



22 

 16 

 14 

 12 



9 



4 



2 



1 



1 



1 



82 



Aug. 13 

 20 



17 



15 



13 



11 



4 



2 



2 



1 



1 



86 



Sept. 25 

 15 



15 



12 



8 



8 



4 



2 



3 







1 



68 



What a happy family this was ! In all this jostle 

 up to the middle of August, during which every plant 

 had increased its bulk from two to twenty times, only 

 the crab grass — apparently the most tenacious of them 

 all — had fallen off ; and yet the area seemed to be full 

 in the beginning ! How, then, if all had grown bigger, 

 could there have been an increase in numbers, or even 

 a maintenance of the original population ? In two 

 ways : First, the plants were of widely different spe- 

 cies of unlike habits, so that one plant could grow in a 

 place where its neighbor could not. Whilst the pigweed 

 was growing tall, the medick was creeping beneath it. 

 This is the law of divergence of character, so well 

 formulated by Darwin. It is a principle of wide appli- 

 cation in agriculture. The farmer "seeds" his wheat - 

 field to clover when it is so full of wheat that no more 

 wheat can grow there, he grows pumpkins in a corn- 

 field which is full of corn, and he grows docks and 

 stick -tights in the thickest orchards. Plants have no 

 doubt adapted themselves directly, in the battle of life, 

 to each other's company. 



