Hair-like Trichomes. 8i 



never protected by similar formations. All that can 

 be said is that such trichomes, when developed on stem 

 or leaves, as a rule fulfil some other function than that 

 of keeping off insects from the flowers ; and on the 

 other hand that when developed inside a flower, their 

 office in the great majority of cases is the exclusion of 

 unbidden guests.-' 



Just as thorns are sometimes to be considered as 

 modified leaves or parts of leaves, at other times as 

 epiblastemes of the epiderm, so also are the hair-like 

 structures in question sometimes to be looked on as 

 parts of a fibrillated petal {Gentiana ciliata, Plate II. 

 fig. 64 ; Tellima grandiflora, Plate II. fig. 75), and 

 sometimes as epiblastemes of the floral organs. In 

 the latter case again they may present themselves as a 



''■ Hair-like trichomes, when inside the flower, have various func- 

 tions. Sometimes they keep the anthers for a time in some fixed 

 position (several species of Euphrasia, Thesium) ; sometimes they 

 cause the discharged poUen to fall in some definite direction 

 (Trixago, Pedicularis, Orobanche) ; sometimes they sweep the 

 pollen out of the tube formed by the anthers (Compositse), or 

 collect the pollen grains (penicillate and feathery stigmas) ; some- 

 times they serve as a bridge for insects, leading them to the right 

 entrance into the flower (Gampanulabarbata), eic, etc. Hair-like 

 formations in many cases are of no use until the process of 

 flowering is over. Such, for instance, is the case with the " weels " 

 in the calyx of Thymus serpyllum ; and such, of course, vidth all the 

 hair-like structures that minister to the dispersal of fruits and 

 seeds. Hair-like trichomes, when on the stem and leaves, in part 

 protect the leaves from too great evaporation ; in part act as a 

 cooling apparatus, inasmuch as by their powerful radiation of heat 

 they bring about condensation of moisture and abundant deposition 

 of dew. 



