Rosaceæ. 125 



observations of insect-visitors, in true Arctic regions, to 

 the species in question, viz. only in the case of Pot. 

 emarginata, Pot. nwea, Pot. emarginata and Dry as, which 

 were visited by flies and other diptera. 

 II. Many of the Arctic Rosaceæ mentioned here have a very 

 considerable area of distribution. Eight of the species arc 

 circumpolar or almost circumpolar — of these P. pulchella 

 and emarginata are distributed only in the Arctic zone; 

 the others extend far southwards, and of these the two 

 bog-plants P. palustris and Rubus chamæmorus are espe- 

 cially confined to the low lands, while the others (P. nwea, 

 maculata, Sibbaldia and Dry as octopetala) are confined to 

 mountainous districts in temperate regions. Pot. tridentata 

 and Pot. Vahliana are also true Arctic species, but their 

 area of distribution is smaller; this is also the case with 

 Dryas integrifolia, which in America, however, has ad- 

 vanced somewhat southwards. Pot. anserina is almost 

 cosmopolitan. According to Wolf the Tertiary circum- 

 polar land was probably the home of the original Poten- 

 tillas, whence they have migrated southwards. He ascribes 

 to those groups, among others to which our Potentillas 

 belongs, a very high age, and regards several as palaeotypic; 

 the majority of the species must be regarded as very old. 

 Dryas octopetala and Sibbaldia procumbens are probably also 

 originally true Arctic forms, which have afterwards ex- 

 tended towards the south. The great Glacial period may 

 have helped them, together with P. nwea and maculata, 

 to cross the Central European low land; they are also 

 very old species. 



Of these species only the following appear to have 

 qualifications for wide fruit-dispersal: P. palustris and 

 P. anserina by the agency of the water, Dryas by the 

 wind and Rubus chamæmorus endozoically. 



Another group of Ihe species in question comprises 



