LEAVES 



573 



FIGS. 816, 817. Multicellular filamen- 

 tous hairs from a leaf of the cineraria 

 (Senecio emeritus): 816, a general view, 

 as seen in cross section, showing several 

 hairs with their whip-like ends, which spread 

 out horizontally, forming cham- 

 bers between the basal portions 

 of the hairs ; note the great length 

 of the hairs in proportion to the 

 leaf diameter ; considerably mag- 

 nified; 817, a single hair; highly 

 magnified. 



the leaf hairs take the form of 

 brown or silvery-gray scales (figs. 

 8 i 8. 819). In scabrous leaves 

 the surface is papillate orjwarty f 

 as in many composites. 



Variations in hair distribution. 

 ".Protective " epidermal hairsj 

 are most abundant jn xerophytes] 

 especially in sandy and rocky 

 regions and in deserts, where 

 they often give a characteristic 

 grayish aspect to the vegetation, 

 as in sage-brush deserts, In 

 alpine and arctic regions and in 

 bogs and salt marshes, hairs are 

 less abundant though by no 

 mean's absent (as in the everlast- 



ings, Ledum, etc.) . Leaves 

 frequently are hairier 

 when young than when 

 mature, many of the hairs 

 soon breaking at a more 

 or less definite weak spot. 

 While some leaves are 

 equally hairy on both FIGS. 818, 819. Multicellular shield-shaped scale 

 surfaces, many leaves are hairs from the leaf of Elaeagnus : 8 1 8, a general view as 

 hairy mainly or only on I seen in cross section, showing the hairs each of which 

 . \consistsofaverticalstalksurmounted by a horizontal 



the under (stoma-bearing)/ scale . considerably magnified; 819, the terminal scale, 

 Surface (as in the silver as seen from above; highly magnified. 



