17 



2b: The secondary bark. 



(compare fig. 129 Pl. XIII, fig. 130. 131. Pl. XIV, 132, 133, 

 134, 135. Pl. XV, 136, 137, 138, 139. Pl. XVI.) As soon 

 as the cambiumcells corne to a period of comparative rest, 

 they contain alcaloid. Those which afterwards differentia- 

 te to cells of the medullary rays, plates or bastparenchy- 

 ma collect more and more alcaloid until they contain 

 large quantities of it. Sieve- tubes, conducting cells and 

 bastfibres contain no alcaloid. This explains why the outer 

 layers of „Cinchonabark" contain more alcaloid than the 

 inner ones do. The vulgus „Cinchonabark" of course con- 

 sists of secundary bark plus primary bark plus corklayers. 

 The primary bark contains, as we saw allready, alcaloid 

 in ail cells except in those which contain oxalic acid and 

 in the „Gummiharzschlaûche" 



The secundary bark on the contrary, consists of paren- 

 chyma containing alcaloid, of barkfibres and sieve -tubes 

 containing none, while the number of sieve -tubes increases 

 the nearer ohe cornes to the cambium. By the continuous 

 originating of new layers between wood and bark, the peri- 

 pheral sieve -tubes become more and more compressed so 

 that finally the most external ones become unrecognisable 

 and hardly occupy any room. If every parenchyma cell con- 

 tains about the same quantity of alcaloid it stands to reason 

 that the secondary part of the bark must contain less al 

 caloid than the outer one, as in the secondary part there is a 

 large tissue, without alcaloid: the sieve -tubes, while no such 

 tissue exsists in the primary part. This resuit is confirined 

 by analysis. Broughton found the following quantities: 



Ginchona succirubra. 



Part belonging to the secondary bark 5. 94°/ G 



„ „ „ primary „ 7. 98 " 



But not only this: on the grounds above mentioned, the 



