THE ANGIOSPERMAE : LEAVES 



1021; 



while its cells serve as channels of transport for materials between the palisade 

 cells and the veins. Anatomically this is illustrated by the system of what 

 are called collecting cells, that is, mushroom-shaped cells, the flattened 



Tyloses 



Fig. 1 014. — Bciheris nervosa. Horizontal section 

 through the spongy mesophyll showing 

 tyloses in the intercellular spaces. {After 

 Wylie.) 



heads of which each make contact with the bases of a group of palisade cells. 

 The relative isolation of palisade cells from each other implies that there 

 can be little, if any, lateral transport between them, and that carbohydrate 



Cork cells 



Cork cambium 



Fig. 1015. — Berberis nervosa. Transverse section through the injured 

 margin of a leaf showing the development of wound cork. {After 

 Wylie.) 



translocation from the palisade layer must be through the base of each cell 

 individually. The rest of the spongy parenchyma forms an anastomosing 

 system of pipe lines connecting with the veins, which are both the source 



