INSECTS. 209 



is it a wonder the canker-worms were scarce for some years 

 succeeding? / 



Many of our most injurious species are imported from 

 abroad, and it frequently happens, very unfortunately, that 

 the species come without l)ringing its' parasites with it, or at 

 least only a part of them. This is undoubtedly the reason 

 these introduced species frequently spread with such alarming 

 rapidity, until at last some of the native parasites attack it 

 and multiply so as to check its increase, or some of its foreign 

 parasites are brought by chance to the rescue. As yet none 

 of the old world parasites of the European cabbage butterfly 

 have been observed to attack it in this country, and native 

 parasites have thus far almost entirely neglected it. This 

 destructive butterfly, supposed to have been introduced at 

 Quebec twelve or fifteen years ago, left thus unresisted, has 

 already spread over all the eastern part of the country. The 

 wheat midge when first it appeared in this country is said to 

 have been free from the attacks of parasites, which accounts 

 for its rapid diffusion and the great extent of the damage 

 which it caused. 



In addition to these more apparent and familiar ways in 

 which insects are beneficial toman, great numbers of species 

 render an essential service — are in fact an absolute necessity 

 — as pollen bearers. This office which insects perform is, I 

 fear, almost entirely overlooked by the farmer, while he owes 

 to its faithful performance the fruitfulness, and in fact the 

 very existence, of many of the crops he cultivates. You are 

 aware that our common plants mature no seed unless some 

 of the pollen, or fecundating dust, is transferred from the 

 anthers, or pollen-producing organs of the flower, to the stig- 

 ma, the organ which receives it and transmits the contents 

 of the grains to the rudimentary little seeds. If this transfer 

 of pollen does not take place, the rudimentary seeds do not 

 go on developing, but perish. In some plants this transfer of 

 pollen is brought about by the wind, but in far the greater 

 number of flov^ering plants, insects are necessary to its ac- 

 complishment ; for experiments have shown that flowers can 

 seldom be fertilized by their own pollen ; they require the pol- 

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