+ ae 
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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