80 THE POPULAR SCIENCE MONTHLY. 



while kept away from others by effective defenses. (Halicta feeds 

 on the' deadly nightshade, which is poisonous to most animals.) 

 I have no doubt that the butterflies, whose wonderful instinct 

 leads them to deposit their eggs upon the plants best adapted to 

 nourish their young, are aided in distinguishing between species 

 and often warned off of the wrong ones by such spots and mark- 

 ings ; for they well know how to put two and two together. 



The coloring matters of plants are closely connected chemically 

 with the aromatic group of substances (Vines). Naturally, then, 

 odor sometimes takes the place and does the work of color. The 

 presence of distasteful oils, resins, etc., is announced by the odor 

 of some plants no less effectively than that of obnoxious tannin, 

 stinging raphides, or bitter alkaloids, by the colors of others. 

 The most brilliant flowers are not the sweetest ; both qualities are 

 not ordinarily needed (though they may exist together, as in the 

 hard-fighting plants of the Mediterranean region) ; 14'6 per cent 

 of the white flowers are odorous, only 3'2 per cent of the red.* 

 And odor, like color, may be at the same time attractive and 

 repellent — a phenomenon probably much more common than we 

 imagine. 



Ten of the thirty species mentioned by Kerner as not eaten by 

 herbivorous mammals are either aromatic or strong-scented. 

 Pasture mints and field onions are avoided by cattle. What 

 hungriest mammal would relish a meal of the skunk-cabbage or 

 the spotted arum ? Yet flies are attracted to both. If the offen- 

 sive odor which some beetles and caterpillars emit when handled 

 is a warning, surely that of these plants says more plainly than 

 words, " Ne mo me impune lacessii." Herbivora seem even to be 

 repelled by the sweet fragrance of wintergreen, lily of the valley, 

 violets, and of some orchids, which attracts to them their insect 

 friends. 



Again, the same animal may be simultaneously attracted and 

 warned by a color. Dr. Ogle found the white and blue varieties 

 of a species of monk's-hood growing in the same district of 

 Switzerland. Almost every opened corolla of the white variety 

 was perforated ; none of the blue. The flowers are dependent for 

 pollination upon bees; the perforated white variety therefore 

 produced no seed, and this form was rare ; but the blue, entered 

 legitimately and abundantly pollinated, common. So the impor- 

 tance of the warning is evident. The blue corolla invites guests 

 to the feast of honey, but at the same time proclaims that it is for 

 their interest to get it lawfully. The bees understand that un- 

 pleasant properties of some kind are associated with the color of 

 this form. 



* Cruger 



