Chap. XXVITI. IN CHINCHONA-BARKS. 490 



tree grows, the larger is tlie proportion of alkaloids contained 

 in the bark ; ^ and that, although the trees growing nearest 

 the plain were generally much larger, yet their bark was by 

 no means so thick in jH'oportion to tlieir diameter as in trees 

 higher up. He adds that, in cutting do^Mi trees in the hot 

 plains, he has often been struck with the thinness of the bark 

 compared to that of trees gi-owing in temperate climates.^ 



There are several other conditions under which the largest 

 amount of alkaloids is formed in chinchona-barks, which 

 are as yet Kttle understood. Dr. Karsten suggests that the 

 content of alkaloids in the same species of chinchona-trees, 

 growing in different ravines, is affected by unceasing mists in 

 one, and constant sunshine resting on the vegetation in the 

 other ; the former impeding, and the latter promoting, the 

 formation of quinine.^ In the Loxa region a great difference 

 has been noticed in the bark of Q. Condaminea, according as 

 the tree has growTi on the sides of the mountains most 

 exposed to the rays of the morning or of the evening sun : 

 and Mr. Spruce remarks of the "red-bark" trees that the 

 ridges on which they grow all deviate from an easterly and 

 westerly direction, and that the trees are far more abundant 

 on their northern than on their southern sloj)es. The northern 

 and eastern sides of the trees had also borne most flowers, 

 and scarcely a capsule ripened on their southern and western 

 sides, except on one tree of more open growth than the rest. 

 This phenomenon is due to the fact that the trees receive 

 more sunshine from the north and east, dming the summer 

 mornings,^ the afternoons being usually foggy. 



All these points will receive careful attention from IMr. 

 jMcIvor, in conducting the cultivation ; and liis observa- 

 tions will soon enable him to decide many points connected 



' Spruce's Report, p. 83. 

 2 Ibirt., p. 27. Sep also Korsten, 

 p. '20. 



3 Karsten, p. 20. 



* Spruce's Report, p. 23. 



2 K 2 



