88 



PALISADE-LAYER 



[OH. 



spaces between them are quite inconsiderable. The pe- 

 culiar shapes and arrangement of these cells suggested 



Fig. 25. Transverse section across a leaf of the Birch, Be tula alba, in 

 the region of the midrib a, and passing through two smaller ribs c and e ; 

 d upper epidermis, beneath which is the palisade-layer ; b gland on lower 

 epidermis ; / stoma leading through the lower epidermis into the inter- 

 cellular spaces of the spongy mesophyll (Ha). 



the name "palisade" for them, and botanists generally 

 speak of this layer of the mesophyll as the palisade- 

 tissue or layer (Fig. 26). 



Now let us observe how different is the state of affairs 



Fig. 26. Semi- diagrammatic view of a leaf in section, showing upper 

 and lower epidermis, the latter with stomata. Between these two layers 

 the mesophyll, the palisade-tissue above, and the spongy tissue below. 

 Two stomata in section show how the intercellular spaces communicate 

 with the external air (G). 



