422 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 



a result than as a cause of excessiv'e dry weather ; and the prevailing 

 belief that large conflagrations or extensive lires are conducive to rain, 

 bears on this point. 



^' 4. Whenever grass is burned during the growing season, the old and 

 drier blade is soon succeeded by a green and succulent one, which has 

 far greater power to attract and retain moisture ; while if burned in 

 winter-time, the evaporation from the soil can be thereby but slightly 

 afl'ected, because of the weakened power of the sun and the snows which 

 usually cover and protect. 



*' 5. Droughts are by no means confined to that portion of the country 

 subject to the locust invasions. 



" 6. The reason why locusts are more sluggish and less inclined to fly 

 at morn than at noon is not so much a question of the comparative 

 density of the atmosphere as of the difference In temperature. All 

 diurnal insects are sluggish in the cool of the morning, and their activity 

 increases with the rising of the thermometer j and flight, whether of 

 bird or insect, is, we conceive, easier, cceteris ])aribus^ in a dense than in 

 an attenuated atmosphere. 



" 7. As the Eocky Mountain locust multiplies continuously in the 

 Permanent region, its descent into the plains and prairies to the east 

 and south, where it does not permanently thrive, cannot well be affected 

 by the burning of the grass on these plains and prairies. 



" From what has preceded we think we may safely conclude that the 

 non-burning of the prairies will have no effect in i^reventing locust 

 injuries, but that, on the contrary, as shown in Chapter XIII, the judi- 

 cious burning of such prairies at the proper time is most beneficial and 

 highly to be commended. 



"Indeed, there is only one way in which there can be any real con- 

 nection between the burning of prairies and the ravages of the Rocky 

 Mountain locust, and that connection is through the remote past, and 

 altogether beyond our present control. In the report of the Chief 

 Signal Officer to the War Department for 1872 will be found an inter- 

 esting account of the great fires of 1871 in the Northwest, in which 

 the late Prof. J. A. Lapham, of Milwaukee, Wis., maintains that our 

 extensive Western prairies and plains owe their existence and origin 

 to the agency of fire. These fires, encouraged by drought, and either 

 kindled by accident or intention, have swept over the country for ages, 

 and while they leave the roots of the grass uninjured, they destroy the 

 germs of most other plants, including forest-trees j and Mr. Lapham 

 pictures to himself a long-past struggle between forest and prairie, in 

 which the latter, by the assistance of the Fire King, has gained and held 

 the vantage-ground. 



" While wo do not jagree with Professor Lapham that the remote 

 cause of our prairies can be attributed to fire, yet no one can doubt its 

 agency at the present time in maintaining these prairies and preventing 

 timber-growth in the more humid portions of the great prairie regions. 



