ENZYME-RESERVOIRS 529 



against snails and other animals has been pointed out by Stahl G. 

 Kraus and others, on the other hand, lay stress upon the antiseptic 

 properties of these compounds. 



3. Enzyme-reservoirs?^ 



In the Cruciferae, Capparidaceae, Tropaeolaceae, Resedaceae 

 and Limnantiiaceae, the ethereal oils which are responsible for the 

 characteristic pungent odour and taste of all the vegetative parts 

 (especially when these are cut or bruised) are never present in the free 

 state in the uninjured plant ; they are only produced as a result of 

 mechanical injury by the action of an enzyme, myrosine, upon a glucoside- 

 like compound, potassium myronate, which is hydrolysed with formation 

 of allyl isothiocyanate (allyl mustard-oil) or a related body, glucose and 

 potassium sulphate. In the intact tissues, according to Guignard, 

 myrosine and potassium myronate are located in different cells, the 

 former being contained in specially differentiated enzyme-reservoirs. 

 These enzyme-cells, which are most often tubular in shape, though 

 other forms also occur, were first discovered in the Cruciferae and 

 Capparidaceae by Heinricher, who termed them " protein-sacs " on 

 account of their microchemical reactions. The fact that they contain 

 myrosine was established later by Guignard. Heating with concen- 

 trated hydrochloric acid, containing a single drop of 10 per cent, 

 watery solution of orcin per c.c, causes the cells in question to assume 

 a violet coloration owing to the presence of the enzyme. The cell-sap 

 of the enzyme-reservoirs is transparent in the living condition of the 

 cell, but coagulates on heating to boiling-point ; whether it contains 

 ordinary protein-material in addition to dissolved enzyme or not, is still 

 uncertain. 



The distribution of myrosine-celh in the vegetative organs of the 

 aforesaid plants is subject to considerable variation. Heinricher's 

 detailed investigations of the Cruciferae have shown that in some 

 species (e.g. Crambe cordifolia) idioblastic myrosine-celh occur in almost 

 every part. In other cases they are principally found in association 

 with the vascular bundles, and in particular with the leptome-strands ; 

 in Moricanclia arvensis, finally, they are all sub-epidermal both in stem 

 and leaf. According to Guignard, these statements also apply to the 

 other families, where, however, the organs in question are chietly 

 located in the cortex of root and stem. 



Another enzyme that is sometimes contained in special reservoirs 

 is emulsin, which hydrolyses the glucoside amygdcdinc present, for 

 instance, in bitter almonds with the formation of hydrocyanic acid, 

 benzaldehydc (oil of bitter almonds) and sugar. In Prunus Lauroccrasus, 

 according to Guignard, the emulsin is mainly contained in the 



