232 ILLINOIS STATE HORTICULTURAL SOCIETY. 



in April, ranging from the 4th to the 29th of the month, and from 

 31° to 11° of the thermometer. In 1874, the temperatures on April 

 29 fell to 28°. In two years of the six — 1861 and 1866 — we had 

 frost in May, and that as late as the 17th, and the lowest temperatures 

 of this month in these years were 30° and 31°. It would thus appear 

 that in our region frost in May is not common, but that it may occur 

 as late as the middle of the month. A more extended series of obser- 

 vations are, however, needed to enable us to arrive at any definite 

 conclusion on the point. As bearing on horticulture, it may here be noted 

 that the depth to which frost penetrates into the ground will vary from 

 year to year, according to the severity of the winter and to the amount of 

 snow that falls. There can, however, be no doubt that in ordinary winters 

 it reaches to the depth of from 2^ to 3 feet; and that in ordinary soils 

 it does not altogether disappear till about the beginning or middle of May. 



From temperature, let us now pass to rain-fall and snow. For the 

 ten years of my observation we have an average of 90^2 days of rain and 

 snow to the year; the maximum being 131, and the minimum 44. Our 

 average snow-fall is 22.07 inches ; the maximum being 35.35 inches, and 

 the minimum 11 inches. This affords us a mean of 2.20 inches of water. 

 Only rarely have we snow either in April or October, and then only in 

 small quantities. January and February are our snow months. Our 

 average annual rain-fall amounts to 34.05 inches (including melted snow). 

 The maximum was 42.84 inches in 1862; and the minimum was 20.35 

 inches in 1870. Of this total the largest amount falls in the six summer 

 months, from April to September, namely, 22.52 inches; and the small- 

 est in the winter months, from October to March, namely, 11.62 inches. 

 The rain and snow days in winter are ^8, and in summer 52. Compared 

 with other places, our rain-fall is about an average. In Chicago it is 23.73 

 inches; Davenport, 25.21; Keokuk, 29.97; Boston, 46.76; New York, 

 42.45; New Orleans, 72.41; Key West, 29.58; Cincinnati, 36.50. Our 

 mean barometer, corrected for temperature and elevation, is 30°. 031. 



These averages, while of service as affording general characteristics 

 of climate, do not avail much in determining the special conditions 

 which affect the growth and health of plants. To obtain a knowledge of 

 these conditions, it is necessary to leave averages and come to specific 

 facts. This will be obvious when we consider that the average annual 

 rain-fall of England is only twenty-five inches, while ours is thirty-three. 

 Yet who can doubt that the climate of England is greatly more humid 

 than ours? Were one to form an opinion on these averages as to which 

 climate was best suited for horticulture, he would not hesitate to prefer 

 Illinois to England ; and yet, in fact, we know that the special conditions 

 under which rain falls in England renders that country greatly superior 

 to ours for horticulture. By this example we are warned not to trust 

 much to averages for our determinations of climate in relation to the 

 growth of plants. Any approximation to certainty can only be reached 

 by a careful consideration for a series of years of the daily observations 

 of the several months of summer. 



It will, perhaps, be enough for tlie purpose of illustration to select 



