20 Knud Jessen. 



placed narrow cells, which to a certain extent are grouped 

 around the bundles. The proportion between the thickness 

 of the leaf and the thickness of the palisade parenchyma is 

 about ^. The spongy parenchyma is built in such 

 a manner, that between the bundles in the middle of the leaf 

 areas occur where the intercellular spaces are very large. 

 This structure has this effect that the thick, solid leaf suc- 

 ceeds in getting a well-developed system of larger canals 

 in the respiratory tissue'. For the rest the spongy paren- 

 chyma consists of rather small cells of simple form (Fig. Q,D). 



The larger vascular bundles are accompanied by bast both 

 upon the upper and the lower surface. The leaves are very rich 

 in sphaero-crystals which occur especially along the bundles. 



When the trifoliolate leaves die, the leaflets fall off sepa- 

 rately, as mentioned above, and leave a scar upon the leaf- 

 stalk which persists upon the rhizome for a year or more. 

 Fig. 6, G shows a median, longitudinal section through a 

 leaf-stalk just below the blade. The leaf-fall is in several 

 ways prepared for through the anatomical structure. The 

 three bundles of the leaf-stalk divide, so that three enter 

 each leaflet. The bundles of the median leaflet are all of 

 almost the same strength, and lie in almost the same plane; 

 in the lateral leaflets the two lateral bundles are very small. 

 In the zone where the leaflet is to be thrown off there is no 

 bast along the bundles, as is the case both in the leaf-stalk 

 proper and along the main bundles of the blade, and the 

 zone in question is further distinguished by a collenchy- 

 matous area which extends straight through the stalk. In 

 the peripheral part of the collenchymatous area the direc- 

 tion of the line of separation is indicated by the longitudinal 

 direction of the cells; thin-walled areas further facilitate the 

 falling process. 



1 Cf. Coptis trifolia. Arct. Flow. PI., I, 6. Ranunculaceæ, by Knud 

 Jessen; Fig. 58, В. Meddel, om Grönland, Bd. 36. 



