CHERRY-LAUREL 



37 



upper surface is dark green and glossy, the under surface paler. In 



outline they vary from oblong-lanceolate to nearly obovate, tapering 



towards both base and apex, the latter being shortly acute and recurved. 



The leaves are thick and coriaceous in texture, and are supported 



on short stout petioles. The margin is slightly recurved and is 



provided at intervals with short strong 



serrations. On the under surface of the 



leaf, near the base, and on either side of 



the midrib are from one to four yellowish 



depressed spots ; these spots are the 



remains of glands in which a sugary sub- 



stance is produced whilst the leaf is 



young. Both surfaces of the- leaf are 



quite glabrous. 



When fresh and entire, cherry-laurel 

 leaves are almost inodorous ; but when 

 crushed, or even scratched with a needle, 

 the young leaves evolve an odour recalling 

 that of oil of bitter almond and hydro- 

 cyanic acid. Old leaves, or dried leaves 

 crushed and moistened with water, yield 

 a much less perceptible odour. 



Constituents. The principal constituent 

 of cherry-laurel leaves is a glucoside. 

 laurocerasin, first isolated by Lehmann 

 (1885), and subsequently by Bourquelot 

 and Herissey, who further investigated it 

 and called it prulaurasin, by which name 

 it is now generally known. Prulaurasin, 

 C 14 H 17 N0 6 , has been obtained in colour- 

 less, odourless, bitter prisms (m.pt. 120 ; 

 O.R. = _53-6). In contact with prunase 

 (an enzyme also contained in the leaves) 



and water, prulaurasin is decomposed, yielding benzaldehyde (oil of 

 bitter almonds), hydrocyanic acid, and dextrose. 



FIG. 25. Cherry-laurel leaf. 

 Under surface. Slightly 

 reduced. 



C 14 H 17 N0 



Prulaurasin 



H 2 = CH0 



Water 



12 



Dextrose 



HCN 



Hydro- 



cyanic 



acid 



C 6 H 5 CHO. 



Benzalde- 

 hyde 



As long as the leaves remain intact no decomposition takes place, 

 for the emulsin is stored in the endodermis of the veins, whilst the 

 prulaurasin is distributed through the parenchyma of the leaf. The 

 two bodies cannot therefore come into contact with one another 

 until the cells containing them are broken ; directly this is effected 

 the reaction takes place. 



