PROF. SNOW ON ENTOMOLOGY. 363 



<or lose its strength under the summer sun, and even if made effectual by 

 frequent renewal, the beetles are left alive to visit other orchards or to de- 

 ^vastate the maples and oaks of our roadsides and forests. This thousand 

 )eetle females, and if we suppose each female to produce fifty eggs we see 

 that by their destruction 25,000 borers have been "nipped in the bud." 



5. The fertilization of plants. It is one of the wonderful facts of natural 

 history that the two great kingdoms of plants and animals are so closely re. 

 lated that each is essential to the existence of the other. That animals 

 could not live without plants, since from these they directly or indirectly 

 derive their sustenance, is really understood. But that plants could not 

 live without animals is a proposition which needs some explanation. Some 

 plants, like the common squash, are so constructed that their staminate and 

 pistillate blossoms are separate from each other. In such cases it is evident 

 that the pollen must be conveyed from the stamens to the pistils by some 

 external agency. This operation, though in some cases performed by the 

 wind, is regularly accomplished by insects, which, in the repeated act of tak- 

 ing honey, convey the pollen from flower to flower,, and thus secure the fer- 

 talization of the ovules. Other plants have perfect blossoms, containing 

 both stamens and pistils, so that it would seem that there would be no need 

 of insect agency to secure the growth of the seed. But it is found that whea 

 these perfect flowers are artificially guarded from the approach of insectih 

 either no seed at all, or else very scanty and imperfect seed are produced* 

 If a portion of a clover field be covered with gauze during the period of 

 bloom so that the humble-bees can obtain no access to the blossoms, no seed 

 whatever will be produced. Yet each clover head has an abundance of sta- 

 mens sind pistils. I observed the maple trees in front of my house (Acer 

 dasycarpum) when in bloom in early spring. One tree had stamens only ; 

 the next tree had perfect blossoms, but the pistils were fully developed and 

 ready to receive pollen while their own stamens were still in a rudimentary 

 condition, and the hive bees were conveying the pollen from the first tree 

 to the second. Two or three days later, when the pistils of the second tree 

 had wilted, its stamens had reached maturity, and the bees were conveying 

 their pollen to the pistils of a third tree. Thus flowers do not furnish honey 

 to insects from purely disinterested motives, but with sweet allurements en- 

 tice them to perform an act essential to the very existence of the vegetable 

 kingdom. 



6, The last benefit derived from insects to which I would briefly invite 

 your attention is the restraining of vegetation within the proper bounds. 



There is no doubt that in a state of nature the kingdom of plants would 

 suffer great deterioriation if the number of individuals was not kept within 

 reasonable limits by insect depredations. By this agency a disastrous crowd- 

 ing of vegetable growth is in a great measure prevented. 



We now pass on to consider the large class of injurious insects. It has 

 been shown that in a natural condition of things, destructive insects have 

 their proper and useful position. But man interferes with the primitive 



I 



