9 



2. The Hypoderm. 



At the upperside of Cinchona leaves a large — celled, 

 colorless subepidermal cell-sheath is obscrved, it is always 

 présent in C. Ledgeriana; in C. succirubra it may be absent 

 over a larger or smaller distance. 



As long as the chlorophyll lias not yet appeared in the 

 very young leaf, this subepidermal layer can not be distin- 

 guished from the other cells anatomatically. But even then it 

 frequently is conspicuous by its large amount of alcaloid. 

 This is also the case in adult leave?; even where it takes 

 trouble to discover the alcaloid in the green cells of a leaf, 

 that leaf will show it plainly in its hypoderm. 



This can be seen very nicely on a tangential section 

 of the upperside of the leaf blade. The finest sections are 

 those where the knife separated exactly the hypoderm 

 from the palisade-parenchyma. Such a section is absolutely 

 colorless and by the action on it of picrid acid the picture 

 becomes very plain indeed. If one regards such a section from 

 above one sees (through the clear layer of epidermal cells 

 with undulated walls) the precipitate in the large poly- 

 gonal straight-walled hypodermal cells. Those hypodermal 

 cells whichcover the leaf-veins are stretched in the direction 

 of thèse veins. Apparently they contain even more alcaloid 

 than the other subepidermal cells. The appearance of the 

 hypodermal cells after the alcaloid has been precipitated 

 in them may be judgeloff by contemplation of fig. 90, 91 Pl. 

 V. fig 96 Pl. VI. fig 98, 99 Pl. VII. 



3. The Mesophyll 



Neither C. C. Ledgeriana, nor C. succirubra, contains 

 any alcaloid in the very young parenchyma; (compare x' 

 in fig 89 Pl. V.) on a somewhat older stage (comp. x. fig - 8 7 

 Pl. IV.) the case alters, it appears gradually and in this stage 

 ail green cells contain it in large quantity (c. fig. 90. Pl. V). 



