408 The Physiology of Plants BOOK in 



galactose, was found in the Kephir organism in 1890 by 

 Beijerinck. 



Three other enzymes acting on varieties of sugar of 

 comparatively rare occurrence are trehalase, raffinase, 

 and melizitase. These were all discovered by Bourquelot 

 in 1893. 



Another group of enzymes which includes a continually 

 increasing number was represented in 1860 only by emulsin 

 and myrosin. We have already alluded to the widespread 

 occurrence of glucosides in plants and to the large number 

 known to exist. Almost every one of them undergoes 

 digestion through the specific action of some particular 

 enzyme, though such action is not so certainly defined as 

 is that of diastase and inulase. Emulsin was discovered 

 in 1837 byLiebig and Woehler; myrosin by Bussy in 1839. 



Liebig and Woehler described the action of emulsin on 

 amygdalin, the glucoside of the bitter almond ; its distribu- 

 tion was further studied by Thome in 1865, Fortes in 1877, 

 and Johannsen in 1887. Our knowledge of it was greatly 

 advanced by the researches of Guignard in 1890, who first 

 determined its exact situation in the tissues of a number 

 of plants. Myrosin was examined by him with even greater 

 minuteness in the years 1890-4. He showed it to be the 

 characteristic enzyme of the Cruciferae and several allied 

 orders. 



Our knowledge of this group of enzymes was greatly 

 increased by the investigations of Bourquelot and his pupils, 

 particularly Herissey, which extended over the last seven 

 or eight years of our period. They discovered a very wide 

 distribution of them among the fungi, and determined that 

 many of these plants contain, either always or under par- 

 ticular circumstances, several of them simultaneously 

 The chief members of the group known in 1900, besides 

 emulsin and myrosin, were rhamnase, discovered by Mar- 

 shall Ward and Dunlop in 1887, gaultherase, or betulase, 



