GEOGRAPHY OF PLANTS 



485 



A comparison of temperatui-es in the valley of the HudsoH may be made 

 with that at several points in the valley of the Mississippi, in Iowa, Illinois, and 

 Missouri, by means of the following tables. Let West Point, in the valley of 

 the Hudson, latitude 41° 23' north, where observations have been made for 

 upwards of 31 years, be compared, as regards the mean temperatures for tho 

 months during which vegetation is active, with old Fort Armstrong, Rock 

 Island, Illinois, latitude 41° 30' north, where observations have been made for 

 upwards of eleven years. 



West Point and Fort Armstrong are in nearly the same latitude, and yet we 

 observe the mean temperatures through the months of April, IMuy, June, July, 

 and August are about three degrees higher at the latter than at the former 

 place. This excess of summer heat in the valley of the Mississippi becomes 

 greater when we compare the valley of the Hudson with points in Illinois and 

 Missouri further south. Such a comparison must be instituted in order to ren- 

 der more plainly apparent the cause of the discrepancy between the grape- 

 growers of diverse opinions residing at the respective localities, whose summer 

 temperatures we propose to compare. Taking West Point again as a repre- 

 sentative of the valley of the Hudson, we have for — 



Here we may observe a diiference of from 6 to 9 degrees of temperature 

 in fiivor of western localities named over those of West Point from April to 

 September, and that Avhile the March mean is somewhat higher in the west, 

 that for April is much greater, thus starting vegetation earlier and urging it 

 more vapidly. This excess is continued through the summer until it is at its 

 height in July; and, while West Point has a mean of but 64. 31^ for Septem- 

 ber, the places named in Illinois and Missouri enjoy a mean heat 4 to ? dcgr^e;S 

 liigher, or that of 68.7° to 73° Fahrenheit, a temperatureadequate to the ripjen- 

 ing of late maturing grapes for which that of West Point is not titt:ed. 



In order more clearly to illustrate the comparative temperatures of the wine 

 districts of Illinois and Missouri, and those of France, Spain, and Italy, we 

 append a table of mean temperatures for sundry places of observation in the 

 latter named countries : 



