SECT.XIY. VEGETABLE WAX. 423 



or wax. Young buds are often covered with resin to 

 protect them from cold and wet during the winter and 

 early spring, as those of the horse-chestnut and balsam 

 poplar. It is wax that gives the bloom to the plum, 

 cherry, and grape, and the rain drops lie on the waxy 

 surface of the cabbage leaf, like balls of diamond, from 

 the total reflection of light at their point of contact. 

 Wax protects plants from damp in a rainy climate, and 

 prevents too strong perspiration from the fleshy leaves 

 of the aloe, cactus, and other inhabitants of the parched 

 and hot regions in the tropics. 



The vegetable substances hitherto under consideration 

 are neutral, but the remarkable compounds albumen, 

 fibrin, and casein, already mentioned as constituents of 

 wheaten flour, not only contain carbon and hydrogen 

 with a little oxygen, but azote and small quantities of 

 sulphur and phosphorus. Each of these three organic 

 compounds is the same, whether derived from animal 

 or vegetable matter. Thus albumen is chemically the 

 same, whether obtained from wheat and other grains, 

 from arrowroot, dahlia roots, the serum of blood, or the 

 white of an egg. As it constitutes the film or thin coat- 

 ing of the primordial cell, and combines with dextrine 

 in its internal viscid lining, it not only forms an ingre- 

 dient in all vegetable organisms, but plays an important 

 part in the growth of the whole vegetable world. 

 Fibrin is chemically the same in the juice of plants and 

 in blood, in which it exists as a liquid during the life of 

 the animal, and as a fibre after death. It forms the 

 basis of the muscular system in animals, and that ex- 

 tracted from the juice of plants coagulates spontaneously 

 like blood. Casein is chemically identical, whether 

 derived from the curd of milk, or from peas and beans. 

 Azote is a very important principle in these substances 

 as well as in the gelatinous substance gluten. It forms 

 an essential part of the animal structure, and is either 

 highly nutritious or deleterious in the vegetable, being 



