418 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



Although climate is the most essential element to be taken into 

 account when the distribution of the plants of any flora is to be considered, 

 yet as that of our own country at the present time is so well known it 

 will be superfluous to describe it in detail.* All that will be necessary is 

 to compare it generally, as being insular and maritime, with that of the 

 Continent, and then to see what differences may be expected to exist 

 between the flora of Great Britain and that of Europe. 



The chief difference between all maritime or insular, and continental 

 climates, lies in the predominance of moisture in the air of the former and 

 in the greater degree of dryness in that of the latter. The immediate 

 effect of watery vapour is to moderate the heat in summer by arresting its 

 passage from the sun, and similarly to arrest its radiation at night and in 

 winter. The consequence is that maritime and insular climates are far 

 less subject to extremes of temperature, diurnal or annual, than are places 

 situate away from a seaboard and many miles in the interior of a 

 continent. Another very important agent in affecting the climate is the 

 prevalence of aerial and ocean currents ; warm in ameliorating, cold 

 in deteriorating it, as far as the magnitude and vitality of any flora may 

 be concerned. This is particularly the case with the British Isles ; for were 

 it not for the warm currents, both of air and water, sweeping past us in a 

 north-easterly direction across the Atlantic, our climate would be very 

 likely to be as inhospitable as is that in the same latitudes of America. 



Perhaps few places could be better chosen to illustrate the above 

 statements than Edinburgh and Moscow. Thus, while the difference 

 between the hottest and coldest months of the year is under 30° for 

 Edinburgh, it amounts to 60° for Moscow ; and it may be added for Nain, 

 on the coast of Labrador, it is 50°, and for Cape Churchill, on the west 

 coast of Hudson's Bay, the difference is even 80°. All the above places 

 are very nearly on the same parallel of latitude. Again, if we take winter 

 and summer temperatures, we find that for July the mean at London is 

 over 62° ; at Berlin, 66° ; at St. Petersburg, 64° ; and at Astrakhan, 77°. 

 While for January at London it is 37° ; at Berlin, 28° ; at St. Petersburg, 

 16° ; and at Astrakhan it is 13°. Similarly in Cumberland (North 

 America), in the latitude of Edinburgh, the winter temperature is —13°, 

 the summer temperature being + 62°. 



If we consider the temperatures of places in the west of Europe, we 

 soon see how important is the influence of warm aerial currents in 

 regulating and ameliorating them ; thus, at Hammerfest (lat. 71°), in Nor- 

 way, the mean winter temperature is 22°, while in the same latitude in 

 Greenland it is 5° below # zero. Again, the temperature at 



* The word climate must be taken to represent the aggregate environment of plants 

 included under 1. Latitude; 2. Elevation above the sea ; 3. Maritime or insular or 

 continental position; 4. Inclination of land ; 5. Mountainous country or otherwise ; 

 0. Character of soil ; 7. Condition of soil, wet or dry, Ac. ; 8. Degree of cultivation ; 

 9. Prevalent winds; 10. Rainfall; 11. Mean summer and mean winter tempera- 

 tures, &c. 



Caithness 

 Labrador 

 Lisbon 



Chesapeake Bay 



58° N.L. is 36° in January 



>J 5> * V 



39 „ 47 



