THE TRIBE OF THE ORx\NGE-TIPS 93 



significant that it has been called "flower picturing." 

 To understand the reason for its existence one has only to 

 watch the butterflies in their native haunts. He will 

 find them flitting from blossom to blossom among the 

 plants of the mustard family — the Cruciferae. This is 

 one of the most characteristic families in the plant world : 

 the foliage for the most part is small and delicate and the 

 flowers have a characteristic four-petaled structure, being 

 practically always of small size and generally toned in 

 whites or yellows. When an Orange-tip is at rest upon 

 these blossoms it merges so completely into the back- 

 ground that it disappears from view. Should a bird chase 

 one of these insects through the air it would see chiefly 

 the orange tips which are so marked upon the upper 

 side of the wing, and when the butterfly closed its 

 wings and lighted among the flowers the orange color 

 would instantly disappear and there would be only an 

 almost invisible surface against the background of flower 

 and leaf. 



The adaptations of these Orange-tips to the conditions of 

 their hves are by no means confined to this remarkable re- 

 semblance to the flowery background. In the case of some 

 species the whole yearly cycle has been adapted to cor- 

 respond to the yearly history of the cruciferous food plant. 

 As is well known many species of the mustard family spring 

 up early in the season, put forth their blossoms which 

 quickly develop into fruits and then die down, the species 

 being carried through untfl the next year by the dormant 

 seeds. In a similar way the Orange-tips feed as cater- 

 pillars upon the host plant through the spring, completing 

 their growth before the plant dies and then changing 

 to chrysahds which remain dormant tlirough summer, 



