13 



116 Pl. X it is always met with, in the small ones it may 

 be absent or présent. 



-The cambium situated between xylem and phloëm usu- 

 aliy contains no alcaloid; yet it is met with occasionally 

 (c. fig. 116. PI X). It is most frequently met in the cam- 

 biumcells forming the prolongation of the medullary rays. 



In ail parenchymacells between xylem and phloem, be 

 they cambiumcells, cells of the pericyle or parenchyma of 

 the phloëm -part alcaloid may be met with; it is never found 

 in the sievetubes nor in the conducting cells and this is a 

 point of some interest. 



The medullary rays of the xylem -part can contain al- 

 caloid but frequently do not (fig. 116 Pl. X is a spot chosen 

 for its large amount of alcaloids). 



The pith- parenchyma contains alcaloid also; cells which 

 contain oxalic acid possess no alcaloid. (fig. 110 Pl. IX). 

 To get good crosssections with the alcaloid in position the 

 leaves were forced to suck in the iodine solution as 

 described before. In using this method one must not 

 loose sight of the fact that the absence of a precipitate 

 in some particular cell does not yet prove that there 

 was no alcaloid in that cell; it being possible that the io- 

 dine solution did not enter it. If the cell under consi- 

 dération contains starch the entrance or non entrance can 

 be easily determined by the blue color of the starch or 

 the absense of that tint. If the starch is not stained blue 

 and consequently the iodine -solution has not entered, 

 longitudinal sections must be made. 



Fig. 110. Pl. IX is made after a crosssection obtained 

 from a leafstalk, which prcviously had sucked in the io- 

 dine solution. Very conspicuous in this section is the 

 halfmoon shape of the precipitate and the fact that insi- 

 de of the vascular-bundle ring this moon is found at 

 the outer cellwall, outside of the bundle-ring at the inner 



