764 



bionomics of Phylloxera previous to 1905 is carefully summarised and 

 the modification of that knowledge due to later researches form the 

 main part of this paper. 



Want of material has greatly hindered research into the fate 

 of the newly born insects derived from the winter-egg. Material 

 could not be obtained in continental Italy, but the nurseries of 

 American vines at Palermo, Modica and Messina provided an 

 abundance. The experiments made by the author with the aid 

 of collaborators were extremely numerous, and were repeated for 

 several years under the most varied conditions. They consisted 

 chiefly in placing bark containing a very large number of winter- 

 eggs, special precautions being taken to prevent their dying, in 

 contact with uninfected European vine stocks, and also with healthy 

 American vine stocks to act as controls. In spring, on the American 

 vines, numerous primary galls, i.e. those produced by the stem-mother, 

 appeared, which proved that the winter- egg had remained alive. The 

 European vines, on the other hand, were almost always exempt. 

 The roots of both kinds were invariably uninjured. It has thus been 

 proved in the most definite manner that in no case can the insect 

 which is newly hatched from the winter-egg live on the roots. If it 

 has the chance of migrating to the young leaves, or to other green 

 parts of the American vine adapted to it, it forms a gall, and here, after 

 having completed four moults, becomes sexually mature and lays its 

 eggs. If it finds itself on the green parts of European vines, or of 

 certain American vines not adapted to its existence, it punctures the 

 plant, but does not succeed in producing a gall, and dies. 



It is necessary to note that the same sorts of vine do not always 

 behave in a similar manner. The stem-mother lays an enormous 

 C[uantity of eggs over a period lasting about a month, which hatch in 

 eight to twelve days. Individuals from eggs laid during the first few 

 weeks all make their way to the leaves, where they may develop. 

 Those from later eggs pass to the roots ; these, however, are generally 

 few in number. It is a remarkable fact that the migration of the 

 newly-hatched individuals to the underground rather than to the 

 aerial portions of the plant, is connected with the presence of easily 

 identifiable morphological characters, so that their destination may be 

 deduced from their appearance. The author therefore assigns different 

 names to the two kinds of newly- hatched individuals. He applies 

 the name neogallicolae-gallicolae to the newly hatched females of 

 gallicolae which will, in their turn, become gallicolae, and that of 

 neogalhcolae-radicolae to the newly hatched females of gallicolae 

 which will become radicolae. The most important practical con- 

 sequence of these observations is that the newly-hatched insect from 

 the winter-egg does not develop on European vines. Exceptional 

 cases are so rare that they may be practically neglected. No differences 

 can be observed between the newly-hatched leaf and root forms with the 

 naked eye, but under the microscope somewhat important structural 

 differences are obvious ; intermediate forms exist, but their history 

 always follows that of the type they most resemble. As the number 

 of generations increases, the quantity of eggs laid by the galhcolae, 

 becomes gradually smaller, and simultaneously, by observing the single, 

 newly-hatched individuals that emerge, the proportion of neogallicolae- 

 gallicolae to neogallicolae-radicolae may be seen to decrease. It has 



