88 



Introduction to Botany. 



chloroplasts lie within cells and close against their walls, 

 and that for the circulation of air there are spaces between 

 the cells which are in communication with the stomata. 

 A reference to Fig. 36 will show the relation of the 



chloroplasts to the rest 

 of the leaf structure. 

 The cells of the upper 

 side of the leaf, termed 

 the palisade cells, are set 

 up in regular order with 

 their long axes parallel 

 to the direction of the 

 incident light ; the chlo- 

 roplasts are embedded 

 in the living substance 

 of the protoplast which 

 lines the cell walls, the 

 remainder of each cell 

 being filled with a wat- 

 ery cell sap. 



The palisade cells are 

 not compacted together, 

 but have air spaces be- 

 tween them communicat- 

 ing with the stomata. 



FIG. 36. 



Cross section of a leaf. /, upper epidermis ; 

 m, stoma in upper epidermis ; n, row of pali- 

 sade cells containing rounded chloroplasts ; 

 i, lower epidermis; k, stoma in lower epi- 

 dermis ; /, spongy parenchyma cells contain- 

 ing chloroplasts ; /, vascular bundle in cross 

 section ; t and u, intercellular spaces. After 

 SACHS. 



The more loosely ar- 

 ranged parenchyma cells 

 on the under side of the leaf, called spongy parenchyma 

 cells, also contain chloroplasts, but they necessarily receive 

 less light than those on the upper side and cannot manu- 

 facture so much food. The vascular bundles are seen to 

 lie at the center of the leaf where they can readily com- 

 municate both with the palisade and spongy parenchyma 



