Page:Encyclopædia Britannica, Ninth Edition, v. 24.djvu/261

Rh VINE in English vim-vies since 1P63. The symptoms of the disease first appeared in France about the same time, in the neighbourhood of Tarascon. From the department of Gard the infection spread south to the sea, and east, west, and north, till the south-eastern corner of France was thoroughly infected. Another centre of infection arose a few years later near Bordeaux in Gironde, whence the disease spread till the whole of the southern half of France was more or less severely attacked. The parasite was first discovered in France in the year 1868. The Phylloxera has spread to Corsica ; it has appeared here and there amongst the vineyards of the Rhine and Switzerland ; it is found in Spain and Portugal, Austria, Hungary, Italy, and Greece ; and in 1885 its presence was discovered in Australia (Victoria), at the Cape of Good Hope, and in Algeria. Hence it is no exaggeration to say that with very few exceptions its distribution is co-extensive with that of the cultivated grape vine. The symptoms of the disease, by means of which an infected spot may be readily recognized, are these. The vines are stunted and bear few leaves, and those small ones, advanced stage, the leaves are dis- eoloured, yellow or reddish, with their vdges turned back, and withered. The grapes are arrested in their growth and their skin is wrinkled. If the roots are examined, numerous fusiform swellings are found upon the smaller rootlets. These are at first yellowish in colour and fleshy ; but as they grow older they become rotten and assume a brown or black colour. If the roots on which these .swellings occur be examined with a lens, a number of minute insects of a yellowish brown colour are ob served ; these are the root -forms {radicola) of Phyl.lnyf.ra (fig. 1) ; they &quot;When the disease reaches an Fig. 1. Fig. 2. Fio. 1. Root-inhabiting form (radicola) of Phylloxera, with proboscis inserted into tissue of root of vine. FIG. 2. Phylloxera. Winged female which lives on leaves and buds of vine, and lays parthogenetieally eggs of two kinds, one developing into a wingless female, the other into a male. are about 8 mm. long, of an oval outline, and with a swollen body. No distinction between head, thorax, and abdomen can ilu; observed. The head bears small ved eyes and a pair of three- jointed antenme, t lie first two joints being short and thick, the third more elon gated, with the end cut off ob- mmimm Hciuely and A ^^ &amp;gt; Y slightly hollowed ^ out. Underneath, between the legs, lies the rostrum, which reaches back to the abdo men. The insect F g- 3 - Fig. 4. is fixed by this Fio. 3. a, Male produced from small egg c, laid by winged rostrum, which is ^ female (fig. 2) ; b, large egg ; c, small egg., , Fio. 4. Wingless female produced from largo egg (fig. 3, ?/), into cue Iaid by winged f ema i e ( fig. 2 ). root of the vine for the purpose of sucking the sap. The abdomen consists of seven segments, and these as well as the anterior segments bear four rows of small tubercles on their dorsal surface. These root-dwelling insects are females, which lay parthenogenetic eggs. The insect is fixed by its proboscis, but moves its abdomen about and lays thirty to forty yellow eggs in small clusters. After the lapse of six, eight, or twelve days, according to the temperature, the larvae hatch out of the eggs. These are light yellow in colour and in appearance resemble their mother, but with relatively larger appendages. They move actively about for a few days and then, having selected a convenient place on the young roots, insert their proboscis and become stationary. They moult five times, becoming with each change of skin darker in colour ; in about three weeks they become adult and capable of laying parthenogenetic eggs. In this way the insect increases with appalling rapidity : it has been calculated that a single mother which dies after laying her eggs in March would have over 25,000,000 descendants by October. If, however, the insect were content with this method of reproduction, the disease could be isolated by surrounding the infected patches with a deep ditch full of some such substance as coal-tar, which would prevent the insects spreading on to the roots of healthy vines. The fertility of the parthenogenetically-produced insects would also diminish after a certain number of generations had been produced. As the summer wears on a second form of insect appears amongst the root-dwellers, though hatched from the same eggs as the form described above. These arc the nymphs, destined to acquire wings ; their body is more slender in outline, and at first they bear well- marked tubercles. After several moults the rudiments of two pairs of wings appear, and then the insect creeps up to the surface of the earth, and on to the vine. Here it undergoes its fifth and last moult, and appears as a winged female, capable of reproducing parthenogenetically. The winged form has a slender body with distinct head (fig. 2). The eyes are well developed, with numerous facets ; the antenna have three joints, the terminal one shaped like that of the root-dwellers. The wings are transparent, with few nervures, and are well adapted for flight. The anterior pair reach far beyond the end of the abdomen ; the posterior are narrower and not so long. These winged forms are about 1 min. long. They fly about from July till October, living upon the sap of the vine, which is sucked up by the rostrum from the leaves or buds. They lay their parthenogenetically-produced eggs in the angles of the veins of the leaves, in the buds, or, if the season is already far advanced, in the bark. In very damp or cold weather the insect remains in the ground near the surface, and deposits its eggs there. The eggs are very few in number and of two sizes, small and large (fig. 4, b and c). From the larger a female (fig. 3) is hatched in eight or ten days, and simultaneously, for the first time in the life-history of the Phylloxera, a male (fig. 4) appears from the smaller egg. Neither male nor female has wings ; the rostrum is replaced by a functionless tubercle ; and there is no alimentary canal. The female is larger than the male and differs from it and the other forms in the last joint of the antenna?. The life of these sexual forms lasts but a few days, and is entirely taken up with reproduc tion. The female is fertilized by the male and three or four days later lays a single egg the winter egg and then dies. This egg is laid in the crevices of the bark of the vine, and as it is protectively coloured it is almost impossible to find it. Here the winter eggs remain undeveloped during the cold months ; but in the following spring, as a rule in the month of April, they give birth to a female insect without wings, which resembles the root-dwelling forms, but has pointed antenna;. These forms are termed the stock-mothers ; they creep into the buds of the vine, and, as these develop into the young leaves, insert their proboscis into the upper side. By this means a gall is produced on the under side of the leaf. The gall is cup-shaped, and its outer surface is crumpled and covered with small warts and hairs. The opening upon the upper surface of the leaf is protected by similar structures. Within this gall the stock- mother lives and surrounds herself with numerous parthenogenetif- ally-produced eggs, sometimes as many as two hundred in a single gall ; these eggs give birth after six or eight days to a numerous progeny (gallieola), some of which form new galls and multiply in the leaves, whilst others descend to the roots and become the root- dwelling forms already described. The galls and the gall-producing form are much commoner in America than in the Old World. Scheme of the Various Forms of Phylloxera vastatrix. A. Root-infesting forms, 9 Winged forms, 9 I Wingless female. I Root-infesting forms, 2&amp;lt;1 generation, 9 I Root-infesting forms, 3d generation, 9 &c. Gall-producing 9 Root-infesting 9 I i ditto. A. The natural enemies of the Phylloxera are few in number : they include some mites, Hoplophora arctata, Thyroglyphus phylloxeras, and the millepede Poly.rcnus lar/urus, which devours the subter ranean forms. Innumerable artifices have been proposed to com bat the terrible disease caused by this minute insect, but none of them seem to be completely successful. As a rule the means sug-