INSECTS AND PLANTS 85 



complicated, and was only fully worked out, after years of 

 painstaking study, by French and American entomologists. 

 During the winter the eggs may be found singly on old 

 wood, etc., and, from these single eggs, the young insects 

 hatch in the spring : in every case they are females, provided 

 with sucking mouths. The newly emerged young at once 

 proceed to the vine leaves, into the tissues of the upper 

 surface of which they insert their beaks and begin to im- 

 bibe the plant juices. The injury to and irritation of the 

 leaf results in the formation of a hollow sac, which almost 

 encloses the insect and appears on the under surface, like 

 a small tumour a gall, in fact. In about fifteen days the 

 female is full-grown. She is a wingless, plump, orange- 

 yellow creature, and is able to produce her eggs partheno- 

 genetically, that is to say, without recourse to a male, and 

 this she does to some purpose, filling the little leaf sac, in 

 which she dwells, with minute yellow eggs, and then she 

 dies. In a little more than a week these eggs hatch, pro- 

 ducing, in every case, females only, which promptly find 

 their way from the gall and infest other parts of the leaf, 

 or other leaves, in exactly the same manner as their parent. 

 This process is repeated again and again, six or seven times 

 during the summer, till the leaves become thickly studded 

 with galls: always the eggs are laid parthenogenetically, 

 always the young are females, and this form of Phylloxera 

 has been called the form of multiplication. When winter 

 approaches, the insects pass down the vine stems to the 

 roots, where they remain dormant till the spring, then they 

 awaken to activity and begin what is termed the form of 

 devastation (fig. 19). Attacking the roots, as they did the 

 leaves, with the formation of galls, irreparable damage is 

 done to the vines. At first the attack has the same effect on 

 the plant as root pruning, and, as a result, a very large crop 

 of grapes may be produced. The continued root injury, 

 coupled with the strain of bearing an exceptionally heavy 

 crop, tells its tale on the plant its leaves turn yellow, and 



