RESULTS OF COMPARATIVE OBSERVATIONS: BAVARIA. 241 



4. Increased warmth in the earth promotes the circulation of the sap 

 an«l the evaporation of water irom the leaves. 



5. Another indirect action of warmth in the earth, in its influence 

 upon vegetable life, is to hiisten the process of dec;iy of organic matter 

 in the soil, so that plants, other ciicumstances being equal, will obtain 

 more nourisbment in a warm soil than in one that is cold. 



C. Different plants require different temperatures for successful 

 growth. Thus rye requires less heat than barley or wheat. But if the 

 warmth of the earth exceeds the maximum needed for a given plant, a 

 diminution of growth is the consequence. The highest temperature at 

 which life can exist in a root is about 105° F. 



7. Upon the awakening of vegetation in the spring, the temperature 

 of the earth has a very important effect upon the germination of seeds. 

 The various grains require at least 42° to 45°, and growth does not 

 begin in most perennial plants until this degree is reached. From this 

 it will be seen that several of the functions of vegetable life do not take 

 place, or act but imperfectly, at a low degree of heat in the earth, and 

 the agriculturist properly seeks the causes of failure in crops, not 

 always in the low temperature of the air, but in that of the soil, es- 

 pecially it prolonged in the spring. Since we know that the warmth of 

 the earth is of great importance in the vital process of plants, the 

 watering of house-plants with water warmed to blood heat has been 

 recommended. A striking instance of the action ot artificial heat upon 

 plant-life is reported by Dr. Aug. Vogel.^ In a garden at Munich two 

 beds of earth were artificially heated through the whole suu)mer by 

 means of a perforated lead i)ipe attached to a steam-boiler and buried 

 four feet in the ground, so that the earth thermometer rose to from 72° 

 to 100° F. The effect was noticed in deep rooting, but more especially 

 in tropical plants, some of which grew to actual monstrosities. By this 

 we are reminded of the horticultural garden near Zwickau (Saxony), 

 where the artificial heat from burning coal-mines is made useful.^ 



Amount of evaporation from a free water surface in the woods, and in the 

 oi)en fields, or influence of the forests upon such evaporation. 



It is important, not only in its climatological relations, as well as in 

 a purely forestal stand-point, to ascertain from exact observations a 

 knowledge of the amount of water evaporated in fhe forest and outside 

 of their influence, because it explains to us many phenomena, and be- 

 cause these observations add much to the determination of the physical 

 influence of the forest upon the air and soil. 



Water evaporates at any degree of temperature. The amount evap- 

 orated on a given area is governed by the temi)erature, as with eacli 

 degree of temperature, only a certain amount of water can assume the 

 form of vapor. The amount of evaporation, therefore, depends chiefly 

 on the existing temperature, and on the amount of vapor already con- 

 tained in the air; next, on the pressure of the air; still more on the 

 removal of vapor, when formed, by currents of air; and lastly, on the 

 size of the water surface exposed to evaporation. 



' Zeitschrift des latidivirthschaftlichen Vei-eines, 1872. 



2 In tbis connectiou we shonld not forget to mention that observations upon the tem- 

 perature of the soil have of late become of more general interest from a siipiiospd con 

 iiectiou with the origin of cholera. In the Zeitschrift fiir Biolorjic {vo]. i\ , 1t'G8), Dr. 

 Dclbruck remarks that not only the moisture of the earth and movement of subterra- 

 nean waters, but also the temperature of the earth, are causes for originating and 

 spreading this epidemic disease, by increasing the decay of organic matters in the soil. 

 (Xote by Dr. Ehermayer.) 



IC F 



