6 



A. BL YTT. 



[No. 8. 



If we were to colour a map according to the places where cer- 

 taiii groups are most copious, we shoiild at once discover that 

 the}^ bad a scattered distribution. We sboiild find the same 

 colour bere aud tbere, in smaller or larger patcbes, hut tliose of 

 the same colour would be separated hy great spaces of a diffe- 

 rent tint. 



At oue time botanists were satisfied witb explaiuing tbe 

 distributiou of species tbrougb soil aud climate, but as tbe study 

 of tbeir appearauce proceeded, it was discovered tbat tbere were 

 great gaps iu tbe extensiou of mauy. Aud tbe gaps were ofteu so 

 great tbat scieutists were obliged to resort to explaiuing tbe 

 same by maiutaiuiug tbat sucb species were created iu places 

 far apart. But siuce tbe doctrine of tbe origin of species by 

 desceut bas been accepted sucb au explauation must be rejected. 

 Tbere remaius, tberefore. only two ways iu wbicb to explain 

 tbese tbings. Eitber wiud, animals, or sea curreuts are capable 

 of carryiug tbe seed of plants at once across sucb large areas, 

 tbat tbe gaps in tbe extensiou can be explained by tbe meaus 

 of transport at work at present, and tbere are even tbose, wbo 

 still believe tbat tbis is tbe case. In certain iustances tbis 

 explauation is indeed tbe only oue possible, wben for instance 

 it coucerns tbe flora and fauna of Oceanic islauds wbicb bave 

 never been counected witb tbe great continents, aud still bave 

 species more or less related to tbose of tbe mainland. But sucb 

 a sudden migration is very improbable, and must even be dis- 

 peused witb altogetber, as we sball presently sbow, wben it is 

 necessary to explain sucb gaps in tbe extensiou of wbole groups 

 of species as tbose we bave poiuted out above in tbe flora of 

 Norway. 



We bave, besides, anotber explauation of tbis problem, first 

 advauced by Sl. Edward Forbes, wbo maintained — in common 

 witb mauy modem botanists — tbat the climatic variations of the 

 Fast are reflected in the fauna and flora of the Present. He 

 was, we believe, tbe first savant wbo demoustrated, tbat tbe 

 Glacial Age bas left its dislinct mark on tbe flora of tbe present 

 day. Arctic species are fouud on mountains iu temperate cli- 



