No. 633] FOOD-PLANTS AND INSECTS 323 



fed upon, varies exceedingly, from 1:100 to 1:1 or even 

 1.6:1 in the case of the Rutacea\ The average is about 

 1 :4, but there is no tendency for the ratios to fall near the 

 mean and their distribution if not a matter of chance, 

 must have been determined in relation to their environ- 

 ment, no doubt to a great extent by their struggle for ex- 

 istence with other plant-eating forms. 



If we examine the food-plants of the genera or higher 

 groups of butterflies, we find that most of them exhibit 

 well-marked preference for certain, usually related 

 plants. The food-plants of the British butterflies are un- 

 usually well known, and Tutt has recently given in his 

 work on " British Butterflies" a digest of their prefer- 

 enees which he finds to be closely similar to those of the 

 nearctic forms previously considered by Scudder. Gath- 

 ering his more definite data together and using his ter- 

 minology for the groups, the food-habits may be tabu- 

 lated as follows : 



