Formed Constituents of Organisms 159 



pounds, and the hydrocarbons that include resins and volatile 

 oils. It is from amongst this large aggregation of compounds 

 that we might well look for substances that could very appropri- 

 ately be called "acquired characters" or, better, "acquired 

 chemical compounds." But further they rarely, if ever, enter 

 into the upbuild or permanent constitution of the plants. They 

 thus constitute the large group that we may designate as 

 accessory cell-contents. Their function is a more or less tem- 

 porary one. For though some, like the glucose derived by 

 decomposition of glucosides, seem at times to become true 

 foods, they most frequently act as defensive compounds that 

 ward off the attack of parasitic fungi, or of the many and 

 diverse animals that might browse on and exterminate the 

 plants that form them. These compounds therefore consti- 

 tute, in a very real sense, the defensive equipment of the plant 

 world. They include also a very large proportion of the definite 

 chemical bodies that seem to be present as such in living plant 

 tissues, but which at the same time may chemically or electro- 

 lytically act and react on each other. Their absence or rarity 

 in animals seems to suggest the difference between a fixed and 

 a motile organism in regard to defensive methods. 



It would be impossible to treat, even cursorily, the extensive 

 series of each group. But their often closely related and yet 

 chemically distinct characters, that are undoubtedly due to 

 gradual substitution changes, evolved during the evolution 

 of one species or genus from another, are well illustrated in 

 some of the glucoside and alkaloid groups, that have been 

 carefully investigated during the past half century by different 

 distinguished "organic" chemists. The rapidly increasing size 

 of the volume, and the condensing type used, in recent works 

 on organic chemistry, testify to the rapid advance in our knowl- 

 edge of these, as well as of allied compounds, that are only 

 artificially produced. 



Though in the above statement we have attached — and 

 justly so — preponderating im])ortance to the accessory ])lant 

 compounds, it should clearly be noted that various parallel, 

 and at times closely related compounds have developed in 



