ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 325 



have not been observed in other conditions in nature. Small, long', 

 clear crystals are formed on vegetation in a clear, moist air by radia- 

 tion. It would be interesting to endeavor experimentally to produce 

 ice crystals of large size by strong electric charges in saturated air 

 below the freezing point and in rapid motion. 



THE BEARING OP ATMOSPHERIC INFLUENCES ON PLANTS. 



The connection between atmospheric conditions and the development 

 of plants, especially of staple crops, is strongly realized by every farmer 

 in countries where weather varies from year to year. But the subject 

 is an immense one, and its branches extend in many directions, some 

 of which have been little explored, and most of which have only recently 

 come under systematic scientific inquiry in a few places. Most valu- 

 able work on agricultural meteorology has been done in the United 

 States, in France, in Germany, and in England. The Climatology of 

 the United States, by Louis Blodgett, published in 1857; The Signal 

 Service Tables of Rainfall and Temperature Compared with Crop Pro- 

 duction; the Compendium of Phenological Observations, by Ihne, in 

 Sweden; the work of Lawes and Gilbert at Rothamsted, in England; 

 Wollney's Researches in Agricultural Physics ; Adamson's and Bous- 

 songault's various and interesting observations on plants; the great 

 work of Sachs on temperature in connection with plant life; and Hoff- 

 man's extensive work in the same field afford an excellent ground for 

 further researches, which ought to be based as far as possible on a 

 common plan and to be both natioual and international. 



As regards temperature, the following points may be considered to 

 have been ascertained with respect certainly to a large number of 

 plants of agricultural value. A particular temperature or a narrow 

 range of temperature within certain limits is required for the quickest 

 germination and most rapid growth of each kind of plant. Growth is 

 retarded in proportion to the deficiency or excess of temperature. For 

 each plant there is a minimum and maximum temperature and a tem- 

 perature most favorable to growth. The sums of the temperature 

 required for a certain growth of similar plants in two places are in 

 proportion to the sum of the temperatures above zero at the places. 

 Plants in high northern latitudes grow more quickly with the same 

 temperature than the same kinds of plants in lower latitudes. Capa- 

 bility of resisting cold seems to increase with the age of the plant, and 

 plants containing much water seem least capable of resistance. Seeds 

 of northern-grown or mountain-grown plants germinate and develop 

 earlier than similar seeds in warmer situations when both are planted 

 together in the warmer place. There must be a maximum fruit forma- 

 tion and growth for some period of time best adapted to the plant or 

 crop. Blossoming and ripening of certain plants, beets and .potatoes, 

 nowever early sown, coincided with that of the planting which took 

 place when the minimum temperature of germination of the plaut had 



