232 



JOURNAL OF ECONOMIC ENTOMOLOGY 



[Vol.7 



certain limits increasing the metabolism of warm blooded animals 

 and decreasing it in cold blooded animals, (d) Decrease of pressure 

 increases evaporation and radiation both of which lower the tem- 

 perature of animal bodies and influence metabolism, as stated 

 under (c). 



4. Conditions which withdraw water from organisms (evaporation 

 as influenced by various factors) influence irritability, activity and 

 length of life history. Thus Hennings found that low humidity 

 increased insect metabolism and Sanderson found that in dry air 

 the optimum temperature of the growth of insects was lower than in 

 moist air. Thus there are no doubt many exceptions to the usual 

 rules as given under 3. Factors probably operate with reference to 

 an optimum. 



From the summary we have noted that water withdrawal is im- 

 portant in itself in many ways. Temperature is a much studied factor 

 chiefly because of the ease with which it is measured in experi- 

 ments with land animals, changes in temperature are always also 

 changes in the rate of evaporation. Evaporation is best measured 

 with the Livingston porous cup atmometers supplied by the Plant 

 World, Tucson, Arizona, and which have proved themselves superior 

 and are now essentially the standard instrument. Table I shows, 

 as measured by these cups, the effect of raising temperature, on humid- 

 ity and evaporation. The latter is nearly doubled by a rise of 16^* 

 C. such as takes place during a few hours of the usual summer day, 



TABLE I.— SHOWING THE EFFECT OF RAISING THE TEMPERATURE UPON HUMIDITY AND EVAP- 

 ORATION UNDER EXPERIMENTAL CONDITIONS. AIR PUMPED FROM A DRY GREEN HOUSE. 

 VELOCITY OF FLOW OVER THE ATMOMETERS ABOUT .104 METER PER SEC. OR 0.2 MILE PER 

 HOUR.i 



1 The atmometers were inclosed in inverted glass jars by means of large corks. The air was forced against the 

 bottoms of the inverted jars from glass tubes just above and a little to one side of the apices of the atmometers 

 and passed over the atmometers and out through an opening 2 inches below the effective portion of the porous 

 cup. Thus the atmometers were not symmetrically exposed, which is usually the case in outdoor exposures. How- 

 ever the three atmometers used gave the same results for the same humidities and rates of movement. Symmet- 

 rical exposure should be attained by use of special glass vessels. 



