228 SPECIAL SECRETIONS. TANNIN. 



the coats of the seed or fruit. Not unfrequently certain little 

 bodies, which have received the name of glands, are seen on the 

 surface of the leaves, from which fluids are poured forth for 

 various purposes. Thus the Nettle is covered with glands of this 

 kind, that secrete an acrid fluid, which, being conveyed through 

 a pointed tubular hair mounted upon the gland, produces an 

 irritation in the wound made by the hair, just as does the 

 poison of the tooth of the serpent or the sting of an insect (. 97). 

 The little Drosera (Sundew) again, exudes a gluey secretion 

 from the surface of its leaves, which serves to attract and retain 

 Insects, the decay of whose bodies seems to contribute to its 

 healthy existence, as it does to that of the Dionaea (. 246). 



364. A detailed account of the various Secretions of plants 

 would not be adapted to this work ; and we shall confine our- 

 selves here to a notice of those, which are most serviceable to 

 mankind. Of all these, there are none which can be at all com- 

 pared in importance w T ith the azotised compounds, chiefly formed 

 in certain seeds, which afford a most important article of food to 

 Animals. These compounds are made up of oxygen, hydrogen, 

 carbon, and nitrogen (or azote), united in the same proportions 

 as those which exist in the Fibrin and Albumen of Animals 

 (ANIM. PHYSIOL., . 21). Several of these azotised secretions, 

 having slight differences in properties, but agreeing in all essen- 

 tial characters, exist in Plants ; and there are few Vegetables, 

 in which some are not to be found. The most important of them 

 are the gluten, which forms a great part of the corn-grains, being 

 especially abundant in Wheat ; and the legumin, which exists 

 largely in the Pea and Bean, and in other seeds of the Leguminous 

 tribe. The great abundance of these principles in the corn-grains 

 and in the seeds of the Leguminosse, renders them peculiarly 

 serviceable as articles of food to Man and Animals ; and we 

 accordingly find, that they have been in cultivation from the 

 earliest period of which we have any historical records. Indeed 

 the original form of the Cerealia (Corn of various kinds) is now 

 completely lost. In the Potato, also, and other tubers and 

 roots which contain starch in large quantities, there is usually 



