20 CONCLUSIOIS^S ON" ANCIEIirT CLIMATES. 



injudicious husbandry, or the diversion or choking up of natural 

 watercourses, it may become more higlily charged with humidity. 

 An increase or diminution of the moisture of a soil almost neces- 

 sarily supposes an elevation or a depression of its winter or its 

 summer heat, and of its extreme if not of its mean annual tem- 

 perature, though such elevation or depression may be so shght as 

 not sensibly to raise or lower the mercury in a thermometer ex- 

 posed to the open air. Any of these causes, more or less humid- 

 ity, or more or less warmth of soil, would affect the growth both 

 of wild and of cultivated vegetation, and consequently, without 

 any appreciable change in atmospheric temperature, precipitation 

 or evaporation, plants of a particular species might cease to be 

 advantageously cultivated where they had once been easily 

 reared.* 



* The soil of newly subdued countries is generally highly favorable to the 

 growth of the fruits of the garden and the orchard, but usually becomes 

 much less so in a very few years. Plums, of many varieties, were formerly 

 grown, in great perfection and abundance, in many parts of New England 

 where at present they can scarcely be reared at all ; and the peach, which, a 

 generation or two ago, succeeded admirably in the southern portion of the 

 same States, has almost ceased to be cultivated there. The disappearance of 

 these fruits is partly due to the ravages of insects, which have in later years 

 attacked them ; but this is evidently by no means the sole, or even the prin- 

 cipal cause of their decay. In these cases, it is not to the exhaustion of 

 the particular acres on which the fruit trees have grown that we are to ascribe 

 their degeneracy, but to a general change in the condition of the soU or the 

 air ; for it is equally impossible to rear them successfully on absolutely new 

 land in the neighborhood of grounds where, not long since, they bore the 

 finest fruit. 



I remember being told, many years ago, by intelligent early settlers of the 

 State of Ohio, that the apple-trees raised there from seed sown soon after the 

 land was cleared, bore fruit in less than half the time required to bring to 

 bearing those reared from seed sown when the ground had been twenty years 

 under cultivation. I can testify from personal recollection that orchards 

 planted by the early settlers in many parts of my native State, Vermont, 

 produced, when they came to bearing, fruit of a quality greatly superior to 

 that borne by the same trees after they were deprived of the shelter of the 

 neighboring forest in consequence of the clearing of the ground for cultiva- 

 tion. I call to mind instances of particular trees whose fruit, originally of 

 great excellence, became almost unpalatable from this cause, or from other 

 influences of rural improvement. For notice of a similar change within the 

 last half century in Scotland, see Nature, Nov. 27, 1873, p. 72. 



Analogous changes occur slowly and almost imperceptibly even in spon- 

 taneous vegetation. In the peat mosses of Denmark, Scotch firs and othei 



