of the Distribution of Arctic Plants, 343 



gory, and it becomes specially important when we consider that 

 so perfect are the arrangements for the migrations of plants, that 

 they will discover and colonise every suitable spot, however small 

 and however distant, and that the strugg-le for existence is really 

 not between one plant and another, but between all plants and 

 external conditions, of which soil is one of the most important. 



Lastly, the actual geographical distribution of Arctic plants is 

 very imperfectly known, except for a limited district in the west 

 of Europe, and the evidence from fossil remains as to the distri- 

 bution in the post-pliocene period is almost nothing. To this must 

 be added the uncertainty that attends the determination of species 

 in the case of plants so widely distributed. Though no one more 

 competent than Dr. Hooker could undertake tlie task of compa- 

 rison and generalistation, we venture to say that every one of his 

 local lists will be open to serious objections and corrections of local 

 botanists, where there are any, and where there are none the risk 

 of error must be ten-fold greater. For example, in a list of a few 

 Greenland species, said to occur only in one other locality beside, 

 we find Potentilla tridentata and Arenaria Greenlandica. The 

 former of these occurs not only in Greenland and Labrador, but 

 in the White Mountains, on the coast of Maine, in Nova Scotia, 

 and various places north of Canada, and it is one of the few spe- 

 cies that are known to have inhabited Canada in the post-pliocene 

 period. The latter is also found on the coast of Maine, and no 

 doubt in many places between that and Greenland. Only a few 

 months ago the discovery of Calluna vulgaris^ the common hea- 

 ther of the old country, was reported in a locality in New Eng- 

 land supposed to have been well explored ; but this plant has been 

 stated to occur in Newfoundland, and many years ago the writer 

 was informed by local collectoi"s that it occurs in Cape Breton. 

 No doubt it may be found along the coast of north-eastern Ame- 

 rica everywhere where conditions are favourable, which can be 

 however only in a few exceptional localities on the coast, and these 

 somewhat out of the way of ordinary collectors. 



In conclusion. Dr. Hooker deserves our thanks for his able 

 and original treatment of his subject; but the problem is very 

 intricate, and we believe that he has not sufficiently weii^hed 

 some of the elements for its solution, and has been disposed in- 

 stead to lean on the hypothesis, which however specious and appa- 

 rently useful in explaining difficulties, has not yet been proved by 

 a single tangible fact, that under certain circumstances two real 



