€2 



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 



Fig. 37. 



A, Climbing hair-cell of Humnlus. B. Climbing: hair-cell of Phaseohis. C, Adjacent margins 

 of two pappus-scales of Galiiiscga pnrviflora. 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 Hippopliae rhamnoides. E, Twining hair-cell of the calyptra of Polytrichum 

 juniperinum. (After Haberlandt. ) 



dew by means of tlie 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 maybe 



