APPENDIX. 



335 



severe cold, it is able to thrive in the climate of the northern tier of states 

 on the one hand and in that of Louisiana, New Mexico, and Southern Cali- 

 fornia on the other. 



NATURAL HISTORY AND HABITS. 



In common with most plant-lice, this species has a complicated life his- 

 tory, some of the details of which are still lackinjr. The common forms 

 both on the roots and above g-round 

 are wingless lice, not exceeding one- 

 tenth of an inch in length, and of a 

 i^eddish-brovvn color, and abundantly 

 covered, especially in the lerial form, 

 with a flocculent waxy excretion. 

 These are so-called agamic females, 

 and reproduce themselves by giving 

 birth, as observed by many entomol- 

 ogists, to living young indefinitely, 

 perhaps for years, without the inter- 

 vention of other forms. The newly 

 born larvae have none of the white 

 excretion, which, however, soon ap- 

 pears as a minute down when they 

 begin to feed. These lice are also 

 peculiar in lacking the honey tubes 

 common to most aphides, but exude 

 the honeydew from the tip of the 

 body. In October or November, or 

 earlier in the south, among the wing- 

 less ones, numbers of winged indi- 

 viduals appear, which are also all 

 females, and are the parents, as 

 shown by the observations, partly 

 unpublished, of Messrs. Howard and 

 Pergande, of a true sexed genera- 

 tion of minute, wingless, larviform Fi 

 lice, the females of which, as in the 

 case of the grape root louse, give 



g. 2 — Woolly aphis (Schizoneura lanif/era. — 

 a, Rootof. young tree illu>;tratin<r deforma- 

 tion- 6, section of root with ajihides clus- 

 tered over it ; c, root louse, female— a and h, 

 natural size ; c, much enlarged (original). 



birth to a single " winter e„„. 

 This egg is attached within a crevice of the bark, and, probably, following 

 the analogy of the phylloxera, hatches in the spring into a female aphid 

 which originates a new aerial colony. 



The winged females appear somewhat abundantly in autumn, and are one 

 of the means of the dispersaFof the insect. They are very minute, clear- 

 winged, gnat-like objects, greenish-brown, almost black in color, with the 

 body covered with more or less of the cottony excretion. 



The aerial colonies are probably killed out every winter in the colder 

 northern districts, but mthe warmer latitudes the partly grown individu- 



