FIELD BOOK OF INSECTS. 



Sprengel, 1793, is credited with having been the first to 

 point out cross-fertilization in plants, but this is a mistake. 

 Thirty years before, Filippo Arena, an Italian, wrote 

 rather fully on the subject and, noting the cross-polli- 

 nation by insects, stated that galls were developed by the 

 plants for the express purpose of having insects ready at 

 hand for the sake of pollination. 



Malpighi, late in the seventeenth century, was the first 

 to record the fact that the production of galls followed the 

 puncture of vegetable tissues by insects, and he came to 

 the conclusion that the insects inject a substance into 

 the plant tissue which produces a swelling similar to that 

 w r hich the sting of a bee causes in animal tissue. Mal- 

 pighi seems to have been correct. At least, we have, as 

 yet, no better explanation of the origin of galls. 



The number of different galls caused by animal parasites 

 runs into thousands. Almost no form of plant life is 

 exempt. Although certain of the higher plants, such as 

 the oak, willow, rose, and goldenrod, are preeminently 

 the gall-bearing plants, still algas, fungi, ferns, and gym- 

 nosperms come in for their share. 



Many of the galls of woody plants have been omitted 

 here, but those of herbaceous plants, including grasses, 

 have been, necessarily, almost ignored. The most con- 

 sistent work with these, chiefly Itonididae, has been done 

 by Dr. E. P. Felt, State Entomologist of New York, to 

 whose papers the student must be referred. The one 

 in the Ottawa Naturalist, Vol. XXV., will be very helpful. 



The notes and illustrations given here are arranged 

 according to the plants on which the galls occur and with 

 but little reference to the relationships of the makers. 

 The illustrations are, for the most part, about half-size. 

 The following list of genera will help to make the relation- 

 ships clear. 



MITES : Acarus, Eriophyes, Phyllocoptes. 

 HOMOPTERA; ApHiDio^E: Chermes, Colopha, Hamamelis- 

 tes, Ilormaphis, Pachypsylla, Pemphigus, Phylloxera. 



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