OEGANS OF NUTRITION. 



131 



Fig. 251. 



( fig. 252, ps), placed perpendicularly to the surface of the leaf ; 

 these cells are also placed closely against each other, and have 

 no intervals but those formed by 

 the unequal contact of such cells, 

 except where stomata occur, 5^,when 

 spaces may be observed, m, m, by 

 which a communication is kept up 

 between the external air and the 

 interior of the leaf. The form and 

 arrangement of the cells beneath 

 the epidermis of the lower surface 

 ei, are entirely different, thus here 

 the cells, pi, are loosely connected 

 and. have numerous large spaces, 1 1, 

 between them; they are also fre- 

 quently very irregular in form, pre- 

 senting commonly two or more pro- y- 

 jecting rays {fig. 251), which be- ' 

 come united with similar projec- 

 tions of the cells next them, and 

 thus leave between them numerous 

 spaces which communicate freely 

 with each other, and form a cavernous or spongiform paren- 



Fig. 252. 



251. Vertical section of a 

 leaf of the White Lily highly 

 magnified, showing the epider- 

 mis of both the upper and lower 

 surfaces, with the intervening' 

 parenchyma. 



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)--r-^\ 





y^ 



Fig. 252. Vertical section of a leaf of the Melon, highly magnified, es. 

 Epidermal tissue of the upper surface, furnished with hairs, p, and 

 stomata, si. ei. Epidermal tissue of the lower surface, ps. Three layers 

 of upper parenchymatous cells, pi. Parenchymatous cells near to the 

 epidermal tissue of the lower surface. fv,fv. Fibro-vascular l)undle3. 

 7n,m. Cavities connected with the stomata. I, I. Cavities between the 

 loose spongiform parenchyma. 



k2 



y 



