STATE HORTICULTURAL SOCIETY. 183 



Usually they are minute in size, and more or less covered with a 

 cottony substance, secreted from the pores of the body. They generally 

 reside on the trunks, stems, twigs or roots of plants, or, if on the leaves, 

 in galls which they produce. Their habits are quite varied, some 

 residing all their lives in colonies on the trunks or larger branches of 

 trees ; others on the twigs or tender shoots of the plants they infest ; 

 others on the roots, coming to the surface only in the winged state, while 

 a few, so far as known, never acquire these organs, and hence are sup- 

 posed to be wholly subterranean ; some pass their entire existence in galls, 

 which they form on leaves or leaf-stems, etc. 



Some carry their wings erect in repose, as those heretofore described, 

 while many rest them horizontally on the abdomen. The veining of the 

 wings also differs considerably, the fore wings in some being similar to 

 the typical form already described, as Fig. I., except that the third dis- 

 coidal or branch vein has but one fork, instead of two ; this form may be 

 seen at Fig. V. ; others have this vein simple, that is, without any fork or 

 branchlet, as Fig. VI. ; while in others the first and second discoidal 

 veins appear to be united and the third wanting, as Fig. VIII., etc. 



Although the double method of reproduction, heretofore described, 

 prevails throughout this division or sub-family, yet the agamic females of 

 some genera always produce eggs instead of larvai, while others bring 

 forth the larvae inclosed in a thin, delicate, membraneous, egg-like sac, 

 which they rupture soon after extrusion, and which may often be seen 

 attached to the tip of the abdomen like a cottony filament. 



The division contains a number of genera, distinguished from each 

 other chiefly by the veining of the wings ; the position of these organs 

 in repose ; the comparative length of the antennee and the number of 

 joints they contain ; and by their habits. But few of the species found 

 in this country have been carefully studied, yet among these are some of 

 the most destructive species belonging to the family, as the notorious 

 Grape Phylloxera, the Woolly Aphis of the apple tree, etc. 



The species of this country, so far as determined, belong chiefly to 

 tlie following genera : Eriosoma, Pemphigus and Phylloxera. A few 

 belonging to the following genera, have also been observed: AJelges, 

 Thalaxes, Chermes, Hormaphis and Rhizobius. 



These genera may be arranged in the following groups, not perhaps 

 with that strict accuracy required by science, but with an approximation 

 sufficient for practical purposes: 



Wings erect in repose — Eriosonia, Pemphigus and Adelges. Wings 

 horizontal in repose — Thalaxes, Chermes, Hormaphis and Phylloxera. 

 Never acquiring wings, so far as known, and living wholly under ground — 

 Rhizobius. 



As the winged specimens are seldom seen, as compared with the 

 apterous individuals observed, we may add that, as a general rule, so far 

 as the species of this country have been observed, these genera may be 

 arranged by their habits as follows : 



Residing on the branches, trunks, or roots, and not forming true 

 galls — Eriosoma, Chermes and Rhizobius. 



