436 THE STRUCTURE OF ECONOMIC PLANTS 



The petiole of the leaf is terete or oval in transection, and the 

 vascular bundles are arranged in a ring with four or five large 

 bundles and several smaller ones constituting the leaf trace. These 

 are surrounded by thin-w^alled parenchyma, and there is an outer 

 zone of small, compact cells in which glands occur similar to those 

 found in the lamina. 



--^^ stoc 



Fig. 114. A, transection of portion of mature leaf through main vein ; B, detail of papillae 

 in nectary: c^, cambium; c«, cuticle; ^/), epidermis ; ^ c, guard cell ; ^/, gland ; wr, mechani- 

 cal cells; ne, leaf nectary; pal, palisade cells; ph, phloem ; spo, sponge cells; sto c, stomatal 

 cavity; xy 1, primary xylem ; xy 2., secondary xylem. 



