466 



ECOLOGICAL GROUPS 



5. Coatings of wax or varnish or incrustations of salts. 



6. Extreme development of the palisade layer. 



7. Reduction of the intercellular spaces. 



8. Mucilaginous, water-retaining cell contents in the spongy 



parenchyma of the 

 leaf (usually in fleshy 

 leaves, Fig. 360). 



9. Permanent verti- 

 cal position of leaves 

 (Figs. 45, 110, 111). 



10. Leaf move- 

 ments, presenting only 





FIG. 361. Cross section of rolled-up leaf of 

 crowberry (Empetrum nigrum) 



Magnified. After Kerner 



the edges to the sun 

 during the heat of the 

 day (Sec. 114). 



11. Rolling up of leaves, either permanent, as in Fig. 361, 

 or temporary, as in Indian corn and in Fig. 362. 



12. Reduction of leaf area, the leaves either few or small, 

 or both. Sometimes the leaf consists of little else besides a 1 

 petiole ; sometimes, as in Figs. 50 and 357, 



foliage leaves are wholly absent. 



FIG. 362. Cross section of leaves of a grass, 1 unrolled for exposure to sun- 

 light and rolled up to prevent evaporation 



r, ridges of the upper epidermis, with many stomata on their surfaces ; e, thick 

 lower epidermis, without stomata. After Kerner 



In regions with a long rainless summer, like that of southern 

 California or the coast of the Mediterranean, many shrubs are 

 summer deciduous, and in their leafless condition the twigs 



1 Stipa capillata. 



