136 



you by tbe statement that hitherto hop-growers have been groping in 

 the dark and working to prevent injuries by applications to the soil. 

 In fact, the English hop growers have been led by their very best au- 

 thorities to waste their energies in this direction. The importance of 

 the matter will appear when I state that the hop crop, which is quite 

 an important one in some parts of this country, and especially impor- 

 tant in some ])arts of Europe, annually suffers from the ravages of this 

 its worst insect enemy, and some years is rendered a total failure by it. 

 Further, that some parts of this country, as the Pacific coast, are yet 

 free from it and that hop growers thereby being forewarned mny pre- 

 vent its introduction from the East or from Europe, as there is very little 

 doubt in my mind but that the insect has been introduced from one 

 country to another in the egg state upon plum scions, as it may easily 

 be transported from place to place in this manner. I had the pleasure 

 during September and the early part of last October to finish up the 

 investigation and follow out the closing scenes in the life history of this 

 species in the county of Kent, England, while some of my assistnnts 

 were doing the same thing in Herkimer County, New York, and the facts 

 independently obtained correspond in a remarkable manner, thus con- 

 firming and strengthening the conclusion which I have indicated to you. 



SUMMARY. 



All three of the species which I have brought to your notice have 

 been imported to this country from other countries, and this is the case 

 with the vast majority of the worst weeds and insects of American 

 agriculture. I should naturally be led, in closing, to some considera- 

 tions growing out of this interesting fact; for it is noteworthy that such 

 introduced species often, and indeed as a rule, outstrip the native spe- 

 cies in the struggle for existence, and become abnormally destructive 

 to cultivated crops. In America and the other newer, but, geologically 

 speaking, older, parts of the world, as Australia, one reason for this 

 state of things is patent, viz, the fact that the natural enemies of the 

 species are, as a rule, not brought with it, so that it has much freer 

 play in its reproductive powers than it has in its native country where 

 such natural checks occur. But there are other just as potent facts 

 which tend to bring about the greater destrnctiveness of introduced 

 species in the countries mentioned, and one that has not been fully 

 realized has always struck me with much force. It is this, that most 

 of such species are introduced from Europe or the older civilizations 

 where, on evolutional grounds, it is natural to sui)pose that they are 

 the very species which have become accustomed to the civilized condi- 

 tions induced during so many centuries. In other words, the species 

 which most abound and have most successfully accommodated them- 

 selves to such artificial conditions, have, in the geologically brief period 

 of man's pre-eminence, acquired advantages over species which have 



