ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 327 



by freezing fog. The southern border, even to some yards' distance, of 

 a thick, high hedge of evergreen, such as holly, is much warmer thau 

 other situations, and is most warm on sloping ground. Pasture land, 

 replacing arable, increases the cold due to radiation at night, and also 

 the relative humidity near the ground, for the dew-point is quickly 

 reached over grass. The difference of temperature between the top of 

 moderately long grass (a few inches) and the surface of the earth or 

 bottom of the blades is often very great in the evening and night, 

 10° or more occasionally, and at 2 inches deep in the ground the tem- 

 perature of the roots of grass, even in England, may be 26° higher 

 than that of the blades. The temperature close to the surface of the 

 earth under grass rises very quickly immediately after sunrise. The 

 temperature at 15 inches deep was high, 59° to 62°, and nearly uniform 

 in August. These experiments were made on sandy soil, and in the 

 mold of a pasture field. 



The relations of the various qualities and conditions of the atmos- 

 phere to plant growth in various soils and situations have still to a 

 great extent to be determined. Agriculture depends not only directly, 

 but also indirectly on weather. A certain kind of season has a com- 

 pound effect on a great number of crops, on each a somewhat different 

 result, and this result has its effect upon the crops of succeeding years. 

 It may be favorable to a weed or to a species of blight, mold, rust, or 

 parasite, as well as to the crop attacked by such pests, and the net gain 

 or loss for the present and future may not be easy to determine. If a 

 particular character of spring is found to have a particular effect, either 

 in hardening a crop for resistance or in developing a pest at some crit- 

 ical time, or in rendering the ground fit for some other crop than one of 

 which the planting seems likely to fail, then valuable results will have 

 been gained. The co-relation of a variety of plants, of birds, of insects, 

 of fungi, with each other, and the relation of each of these to weather 

 and season, have still, for the most part, to be made out. Accurate obser- 

 vations of the times of planting, the times of gathering, and the charac- 

 ter of seasons, may render it possible for specialists to inform farmers 

 with a large percentage of success of the best time for their operations 

 in various localities. Weather conditions are exceedingly important 

 in the cutting and carrying of certain crops — hay, for instance, and 

 there must be a particular time of the summer which is most favor- 

 able for each district, in view of which grass should be sown and cut, 

 without, of course, any interference with the individual judgment as 

 to the right time, which must vary with the aspect of weather and 

 crop. It would be desirable to use so-.ne standard method of obtaining 

 the actual temperature of plants at a little height above the ground, 

 as well as in their roots. The amounts of rainfall and the relation to 

 plant growth in various soils should be systematically recorded. The 

 amount of sunlight and "actinic" energy with relation to various 

 crops has still to be investigated on a large scale; some valuable 

 results have already been obtained. 



