126 BIOLOGY OF PLANTS. 



Calendulin is a peculiar principle found in the marigold ; it 

 is a yellowish, translucent, brittle substance. 



Saponin is another peculiar principle, found in a root which 

 grows in Greece and eastern countries ; it may be used for 

 soap. 



4. Glutinous substances. When wheat-flour is kneaded into 

 paste with a little water, it forms an elastic, soft and ductile 

 mass. When this is washed under a stream of water until it 

 runs off colorless, there remains a tough, elastic substance, of a 

 gray color, called gluten. It was discovered in 1742, by Bec- 

 caria, an Italian philosopher. It has scarcely any taste, and 

 adheres tenaciously to most bodies with which it is brought in 

 contact. It is the substance which renders bread tough, and 

 enables the dough to rise by ferments. It exists in all kinds of 

 grain, and their value depends upon its quantity. Modern 

 chemists hiive resolved it into four distinct principles, albumen, 

 emulsin, mucin and glutin. 



Vegetable albumen is obtained by digesting the gluten of wheat 

 in alcohol, until everything soluble is taken up. It is a bulky 

 substance of a greyish color, soluble in water, and is the sub- 

 stance in the seed, which takes an important part in germina- 

 tion. 



Emulsin (C'^^H^SN^O^) is found principally in almonds, and 

 resembles starch, when dissolved in water. It has the pecu- 

 liar property of decomposing amygdalin, and of forming hydro- 

 cyanic acid, and the volatile oil of bitter almonds. 



Mucin is taken up by hot alcohol, when the gluten of wheat 

 is put into it. It burns like animal matter, and is more soluble 

 than gluten. 



Glutin (C^J^H'^'NiO^) is also taken up by boiling alcohol with 

 the gluten of wheat, and is obtained after precipitating all the 

 mucin. It is a yellow, translucent substance, almost insoluble 

 in water, and generally exists in wheat in connection with 

 starch. 



Zein is a name given to the gluten of zea mais, or Indian 

 corn. It differs from the gluten of wheat by containing less 

 nitrogen. 



Viscin (C^^WK)'^) is a soft elastic substance, of a brown 

 color, identical with bird-lime. It adheres firmly to the fingers 

 like glue, and exists in several species oi' acacia. 



Pollenin (C'^H^OOI^) is derived from the pollen of the pinus, 

 abies and sylvtstris, and is sui)j)osed to characterize every spe- 

 cies of pollen. 



