GEOGRAPHY OF PLANTS. 505' 



and ill May twenty-four cloudy days were observed, and in June ten days of 

 obscure sky. This excess of rain was not confined to Ohio, but was felt in all 

 the •western States. The consequences of this excess of moisture, obscured 

 sky, and high heats, were the general destruction of the crops of wheat and 

 oats, by a blight or rust on the wheat and a mould on the oats. The last expe- 

 rienced a total failure in three-fourths of all the fields in the valley of the Ohio, 

 those only that escaped were on high ground or had been sowed early. Many 

 fields of wheat were not reaped, but were left to decay, and were plouglied un- 

 der for the benefit of the succeeding crop.* 



From the study of many facts connected with the growth of wheat in tem- 

 perate and tropical climates, we are led to believe that in the United States the 

 only positive limit to its cultivation on the south is the northern bounds of hu- 

 mid tropical heats, while on the north it may be grown to the utmost northern 

 extremity of Maine, latitude 47^ 30', where the mean temperature for May, 

 June, and July is but 56.11°, and that for the warmest month, July, 62.30° 

 Fahrenheit. The northern boundaries of the United States are, however, by 

 no means the northern limit of its culture. Wheat is grown on the Saskatche- 

 wan river, in the territories of the Hudson Bay Company, near Lake Win- 

 nipeg, in latitude 54° north, wliere the months of May, June, and July have a 

 mean temperature of 57.11°, and July enjoys a mean of 61.8°. 



On the plains of Bogota, where the temperature rarely exceeds 59°, wheat 

 is reaped in 147 days, having been sown in February and harvested the last 

 week of July, tlie mean temperature for the entire period having been 58° and 

 59°. At Quinchuqui the vegetation of wheat begins in February and ends in 

 July, at a mean temperature of between 57° and 58° Fahrenheit. In England 

 the summer of 18.53 was in many places at too low a temperature to ripen 

 wheat, and the deficiency was general, and said to have been from one-third to 

 one-half of the usual product. The mean for the months of July and August 

 were 51° and 59°, respectively, or two degrees below the usual average. From 

 the above comparison of data it appears that wheat cannot be successfully 

 grown where the warmest month of its growth, or that wherein the grain ia 

 maturing, falls below 60°, or the mean of its period of growth below 56°. 



The author of a paper on the "Effect of Temperature on Cultivation," read 

 at a meeting of the London Central Farmers' Club, a resume of which appears 

 in "The Country Gentleman" for June 11, 1863, states that in England the 

 wheat required, in 1860, 145 days from the first growth to maturity, March 28 

 to August 20, of which 133 days were actual growing days, having a mean 

 temperature above 42°. In 1861, 130 days were required, during which period 

 no mean below 42° occurred, this being, in his opinion, the minimum at which 

 the vegetation of wheat will continue active. The experiments of this writer, 

 continued through several yeai's, result in the opinion that when the tempera- 

 ture of the soil, during the period included between the time of earing and ma- 

 turity, falls below 58° to 60° no progress can be made, and unless 60° is ex- 

 ceeded the crop never fanly rii^eus. 



The above appear to accord closely with the requirements of the whekt- 

 plant in the United States. Those places where the mean for May generally 

 falls below 58° and 60° are the New England States and New York, except a 

 few places in tlie valley of the Hudson and in the southeastern extremity of 

 the State, most of Pennsylvania and New Jersey, except the southern partes, 

 all of Minnesota, Wisconsin, Iowa, Michigan, northern Illinois, northern In- 

 diana, northern Ohio, and in all these districts the wheat crop cannot mature 

 in May. The June mean for most of the districts named is, with few excep- 

 tions, such as Washington county, Maine, which is in the extreme eastern part 

 and much exposed to fogs, also some sections of Vermont, Minnesota, and 



* Silliman's Journal of Science, N. S., vol. XXVII, pp. 216-217. 



