VOL- II.] Phylloxei'ci. 307 



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a generation of winged males are not known. In Solenobia I 

 found in one locality the same species regularly producing the 

 winged male, in another locality the larvae without exception de- 

 veloped into parthenogenetic females. In the first locality the fences 



J 



on which the larvae fed had a covering of Palmella, variegated with 

 isolated patches of Parmelia, and similar lichens. In the second 

 locality, fences and trunks of trees were covered by a luxuriant 

 vegetation of Evernia, Usnea, Cladonia, etc. The sack-bearing larvae 

 collected in the locality produced only females, never yielded any 



male. 



We know but few instances of this form of dimorphism amongst 

 animals, but in the vegetable kingdom the thallophytes abound in 

 analogous cases. Penicillium develops its sexual generation only 



when deprived of the regular supply of oxygen of the atmosphere. 

 A majority of Confervae form the product of sexual combination, 

 the teleutospore only when by the evaporation of water their ex- 

 istence become questionable. Nature does most for the preserva- 

 tion of the species when the existence of the individual becomes 



questionable. 



We do not know the exact circumstances which in one locality 

 produces in Solenobia and analogous cases an endless series of wing- 

 less females propagating like Aphidians by parthenogenis, when 

 in another locality the regular development of the winged male 

 takes place. But it is very probable that the abundant food in one 

 case IS not favorable to sexual reproduction, the scarcity of food 

 and perhaps its inferior quality in the other locality are, it may be, 

 the cause of the more energetic form of propagation. 



In the case of Phylloxera the inferior kind of food, the dying 

 grape roots in the glass jar, or in the infested vineyard, evidently 

 have a great deal to do with the development of the winged genera- 

 tion. There is a second factor in the case of the Phylloxera that 

 favors the development of wings, /. e,y the necessity of preserving 

 the species by the formation of a new colony on sound grape 



roots. 



This is perhaps the cause of the winged generation having been 

 developed by the Phylloxera, not sexual itself, but carrying eggs 

 of two different sizes, analagous to the raacrospores and miscros- 

 pores of the Selaginella. The small eggs analogous to the micros- 

 pore produce males, the larger eggs analogous to the macrospore 

 produce the one-ovuled female. 



