MORPHOLOGY OF HIGHER PLANTS. 179 



oils are stained red by alcoholic solutions of alkanet, and some of 

 them by certain of the aniline dyes, as fuchsin. The distinctive 

 test for the resins is that when treated with concentrated aqueous 

 solutions of copper acetate they acquire a green color. They are 

 likewise stained by many of the aniline dyes. The reserve or fixed 

 oils are liberated as oily globules on treatment of sections with 

 sulphuric acid or concentrated chloral solution. 



The volatile oils are not infrequently associated with other 

 substances of the plant cell in varying proportions, as resins, gums, 

 cinnamic and benzoic acids. Those products which consist chiefly 

 of oil and resin are known as oleo-resins, and include turpentine 

 and copaiba; those consisting chiefly of gum and resin and con- 

 taining but little volatile oil, are known as gum-resins, and in- 

 clude ammoniac, asafetida, galbanum and myrrh ; oleo-resins asso- 

 ciated with aromatic acids are known as balsams, as balsam of 

 tolu, balsam of Peru, storax and benzoin, which latter is usually 

 called a balsamic resin. 



The enzymes or ferments form a group of proteid sub- 

 stances which bring about certain decompositions in the food 

 substances in plants previous to their assimilation, and are of quite 

 general distribution in both lower and higher plants. They have 

 received different names according to the class of substances 

 which they decompose. Thus, those acting upon starch in chang- 

 ing it to sugar are known as diastases. Those which change cane 

 sugar into dextrose are known as invertases (or invertins), 

 while those which act on proteids are called proteolytic. 



One of the interesting properties of the ferments is that in 

 comparison with the amount of ferment employed the product 

 formed through its influence is very large. Thus it is stated that 

 diastase is able to hydrolize 10,000 times its own bulk of starch. 

 Results of this kind are considered to be due to a catalytic action 

 of the ferments, i.e., their power of inducing chemical reactions 

 by their mere presence without themselves entering into the 

 products formed. The ferments require specific temperatures for 

 their action, as, for example, emulsin or sinaptase, which decom- 

 poses a number of the glucosides at a temperature of 35" to 40° 

 C, while diastase, the ferment of germinating seeds, requires a 

 somewhat higher temperature, namely, 50° to 70° C. 



