48 INvSECTS 



for at any time during the summer the underground 

 forms may lay eggs of two sizes producing similar sexed 

 forms that act precisely as did those above ground. 

 So, some of the parthenogenetic forms may leave the 

 roots and crawl up the stem to the foliage, where their 

 progeny form those characteristic galls which strike ter- 

 ror into the heart of the European viticulturist, while 

 they are frequently not even recognized by the vine- 

 grower of the eastern United States. Nor is this leaf- 

 form a necessary feature in the cycle and it does not 

 occur in all localities, so that outward indications of 

 Phylloxera infestation may be completely lacking ex- 

 cept in the condition of the vine. The Phylloxera are 

 gall-makers as a rule, and on the roots of grape pro- 

 duce swellings and distortions which, on vines not 

 accustomed to them, result in the death of the roots 

 or serious disturbance in function, so that the vines 

 sicken and may die. In the original home of the species 

 in eastern North America no especial injury is caused; 

 on the Pacific Coast injury may be severe, but the 

 insect does not spread readily, and so its march may 

 be checked; while in European countries the native 

 vines succumb very easily to the attack of the insect 

 and its spread is rapid where energetic measures for 

 its destruction are not resorted to. 



There are other species of plant lice producing galls: 

 some on hickory make bladder-like structures of con- 

 siderable size, and others produce ridges aptly com- 

 pared to a cock's comb, on elm. In fact, from the 

 simple distortion produced by a feeding along the veins 

 on the under side, to characteristic bladder-like struct- 

 ures, every sort of intermediate form exists, and as 

 a rule these produce no very serious results on the 

 plant. It is astonishing how great a number of such 

 insects a plant may support without interfering with 



