THE USES OF HAIRS. 



23 



view as in the hairs. For on the one hand we find them peculiar and constant 

 in form in nearly whole families — e.g. the large bristle hairs of the Boragtnecc, 

 the stellate hairs of the Cruci/ero', the tufted hairs of the Malvacece and so 

 forth — without our being able to assign any use for them to the plant concerned. 

 On the other hand, we find a great variety of forms of hairs, the biological 

 significance of which can scarcely be doubtful, and the presence of which varies 

 within closely allied groups. Among the simplest, and yet most important forms 

 of hairs, are the root-hairs, already mentioned; these are mere protuberances 



FIG. 126.—-^ stellate hair on the calyx of a young flower-bud of Althcra rosea: thicker projections 

 of protoplasm he on the wall of each cell, and are in 'streaming' motion (indicated by the arrows); 

 B epidermis (ep) with the basal portion of a fully developed stellate hair, showing the structure of 

 the wall (X 55°)- 



of the superficial cells of the roots which grow out into long tubes, and which, as has 

 been already shown, play such a very important part (in the land-plants especially) in 

 the taking up of water and mineral nutritive matters. Much more various are the 

 physiological uses of hairs on the aerial, shoots, on leaves as well as shoot-axes. 

 There we find in the first place hairs of the simplest structure, as long, twisted, 

 thin-walled vesicles very soon losing their fluid contents, — the woolly hairs, which 

 form woolly coverings on the young parts of shoots before their complete develop- 

 ment, and are thus to be looked upon as means of protection for the parts of the 

 bud against injurious external influences ; such hairy coverings are found, for ex- 

 ample, on the unfolding buds of the Horse-chestnut, Alpine-rose, various Aralias, etc. 



