24 Flowers and their Unbidden Guests. 



pollen, the tension of the corolla diminishes. The upper 

 and lower lips separate from each other by a fissure, 

 six mm. long on the sides and one mm. wide at the 

 extremity ; and through this ants can now make their 

 way and carry off the nectar, which has ceased to have 

 any functional significance. I have convinced myself 

 that, as a matter of fact, they do so. 



In bringing this chapter to an end, I may, in addition 

 to the ants, make special mention of the physopodous 

 thrips, which are found almost universally-^ in flowers. 

 These have been regarded by some writers as injurious, 

 by others as welcome, visitors. In my opinion they may 

 be either. Their visits are injurious if, after ran- 

 sacking a flower and quitting it, their further progress 

 does not bring them to a second flower of the same 

 species, or only brings them to it aftpr a long circuit ; 

 in short, if they behave like other wingless insects. 

 On the other hand, their visits are profitable, if, after 

 rifling one flower, they pass over with its pollen to 

 another similar one ; behave, that is, exactly like flying 

 insects, and, like them, bring about intercrossing. As 



^ I foimd them in the majority of flowers on the sea-coast and 

 in the Paszten district in Hungary, no less than in the High Alps 

 on the limits of eternal snow. They slip through the narrowest 

 fissures, and are not kept bact by hairs, even when growing very 

 closely together, so long as these hairs are not sticky. Even close 

 above the nectariferous base of the spur of Gentranthaa rvher L., 

 which could only be reached through a channel scarcely 0'8 mm. 

 in width and 12 mm. in length, the inner side of which is covered 

 all over with little hairs (see Plate III. figs. 97, 98), I still found 

 thrips. 



