Ethereal Oils. 39 



ferrugineum, and species of Polytrichum — plants, one 

 and allj of which the leaves and blossoms alike are 

 unpalatable to grazing animals. 



The substances which make the flowers nauseous 

 to many animals, and by which ruminants in par- 

 ticular are kept from them, are sometimes alkaloids, 

 sometimes resins, but chiefly ethereal oils. But just 

 as those green leaves which contain any of these sub- 

 stances afford welcome food to one animal and un- 

 welcome food to another, so also are the floral organs, 

 when their juices are of this character, repulsive only 

 to certain animals. To others they are not so ; nay, 

 it is unquestionable that ethereal oils exhaled by a 

 blossom, and perceptible from afar, though offensive to 

 ruminants, serve as an attraction to other animals, 

 especially to insects, and allure them to the blossoms 

 from a distance. 



It is worthy of remark that the chemical com- 

 pounds which prevent many animals from touching 

 fresh flowers are either volatilised, or undergo change, 

 when the petals are dried. Many flowers, when dried, 

 lose their special scent, or change it, and mixed in the 

 hay are eaten by ruminants without hesitation. 



2. Access to the Flowers imjpeded ly Isolation in Water. 



Gardeners are well acquainted with a simple 

 method of keeping off ants and woodlice from such 



