clxxxviii 



ated object is observed with colored glasses. Look with the right 

 eye through red glass and with the left through green glass. The 

 sensations of red and green gradually become more feeble. To 

 the eye thus fatigued by green, white would appear tinged with 

 red, and a red color would appear strengthened. To the eye 

 fatigued by red, white would appear tinged with green, and a 

 green color would appear strengthened. If now both eyes are 

 transferred to the red glass, these effects can be brought out in a 

 very striking manner by opening and closing each eye alternately. 

 The converse effects are of course observed by placing both eyes 

 before the green glass. The best object for obsei'vations of this 

 kind is a brilliantly illuminated (white) cumulous cloud. 



Mr. Riley remarked that among the changes that took place in 

 those portions of the State so thoroughly devastated by locusts 

 last spring, none were more interesting than the wide-spread 

 appearance of a grass unnoticed in ordinary seasons. This grass 

 is the Vilfa vagin(Ejlora^ an annual which, as he was informed 

 by Dr. Engelmann, is common from the Atlantic to the Rocky 

 Mountains. The locusts eat down the blue grass so closely that 

 in most instances it dies out, and this annual grass takes its place 

 and grows up rapidly just at the time when most needed by stock, 

 so that it is considered a God-send by the farmers, who generally 

 believe that it was brought by the locusts. The seed was scat- 

 tered over the land the fall before, and the conditions were all 

 favorable for its starting. In ordinary seasons, on the contrary, 

 it is smothered and choked down by other plants. It was a beau- 

 tiful illustration of what Darwin has called "the struggle for ex- 

 istence." He added other facts of a similar nature and showed 

 how a certain large worm {^Deilefhila lineata^ figured and 

 treated of in the 3rd Mo. Ent. Rep., pp. 140-42) which feeds on 

 purslane was from similar causes also unusually numerous. 



Dr. G. Engelmann remarked that these instances of the abnor- 

 mal multiplication of a species in exceptional years were very 

 interesting, and that the unusually wet season and other favorable 

 conditions helped to give the grass mentioned so wide-spread a 

 growth, . 



Judge Holmes objected to the term "struggle for existence," as 

 if a plant could struggle. If it be intended literally, either it is 

 asserted that a plant thinks and wills, or it is asserted that an 



