THE VOLATILE PART OF PLANTS. 105 



structs these substances, and places them at the disposal 

 of the animal. 



The albuminoids are mostly capable of existing in the 

 liquid or soluble state, and thus admit of distribution 

 throughout the entire animal body, as blood, etc. They 

 likewise readily assume the solid condition, thus becoming 

 more permanent parts of the living organism, as well as 

 capable of indefinite preservation for food in the seeds and 

 other edible parts of plants. 



Complexity of Constitution. — The albuminoids are high- 

 ly complex in their chemical constitution. This fact is 

 shown as well by the multiplicity of substances which may 

 be produced from them by destructive and decomposing 

 processes, as by the ease with which they are broken up 

 into other and simpler compounds. Subjected in the solu- 

 ble or moist state to the action of warm air, they speedily 

 decompose or putrefy, yielding a large variety of products. 

 Heated with acids, alkalies, and oxidizing agents, they all 

 give origin to the same or to analogous products, among 

 which no less than twenty different compounds have been 

 distinguished. 



Occurrence in Plants — Aleurone. — It is only in the old 

 and virtually dead parts of a living plant that albuminoids 

 are ever wanting. In the young and growing organs they 

 are abundant, and exist dissolved in the sap or juices. 

 They are especially abundant in seeds, and here they are 

 deposited in an organized form, chiefly in grains similar to 

 those of starch, and are nearly or altogether insoluble in 

 water. 



These grains of albuminoid matter are not, m many 

 cases at least, pure albuminoids. They appear to contain 

 vegetable albumin, casein, fibrin, etc., associated together, 

 though, in general, casein and fibrin are largely predomi- 

 nant. Hartig, who first described them minutely, has dis- 

 tinguished them by the name aleurone, a term which we 

 may conveniently employ. By the word aleurone is not 

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