62 COMPENDIUM OF GENERAL BOTANY. 



vegetation to the most suitable period of the year, will first be con- 

 sidered. The formation of roots reaching deep into the soil, the 

 surrounding of the roots with sand and particles of earth by means 

 of the root-hairs, which usually serve to take up food materials, the 

 hygroscopic salts mentioned on page 56, the retention of rain and 



A, Climbing hair-cell of Humulus. 



FIG. 37. 



7?, Climbing hair-cell of Phaseolus. C, Adjacent margins 



of two pappus-scales of Galinsfga parviflora. Ca, hair-cell of Urtica urens ; Cb, upper 

 end of the same ; Cc, the same with tip removed at z. D, Scaly compound hair-cell from 

 the leaf of Hippophae rhamnoides. E, Twining hair-cell of the calyptra of Polytrichum 

 juniperinum. (After Haberlandt.) 



dew by means of the trichomes, must all be considered as means to 

 the end under consideration. Along with these structural arrange- 

 ments especially the arrangement for the taking up of water there 

 are also adjustments for retarding the loss of moisture, such as the 

 reduction of the evaporating surfaces ; the leaf-formation may be 



