NATURE 



[Nov. 5, 1874 



past season, die off, leaving only young insects, which, as 

 we have said, turn to a copper-brown colour at this 

 period, renewing their light yellow tint in the spring. The 

 Phylloxeras do not increase much in numbers during the 

 months of April and May, but an extensive reproduction 

 of the insect is clearly marked in June and July, while it 

 assumes prodigious proportions in August and September, 

 in the latter months often covering the root-shoots in a 

 continuous mass, so as to make them appear completely 

 yellow with their bodies. In observing the spots attacked 

 by the Phylloxera, two varieties of the insect — a winged 

 and a wingless — have been generally found ; but it would 

 seem (though on this point the reports before us are not 

 cjuite clear) that the one is but a later development of the 

 other. The wings of the Phylloxera do not appear to be 

 capable of sustained flight, but probably help to carry the 

 insect along from place to place when exposed to the 

 action of the wind, for several specimens of the winged 

 variety have been discovered caught in spiders' webs. Of 

 course the winged Phylloxera spreads over the vineyards, 

 which it attacks without any regard to the nature of the 

 soil, whereas the wingless variety is much affected in its 

 movements, and the extension of its ravages is largely 

 determined by the quality of the ground and the nature 

 of the obstacles to which it is exposed. Passing by, for 

 the present, the observations made on this point, we may 

 say generally that the insect would seem to have no 

 burrowing power, but moves from place to place, from 

 root to root, along the line of the fissures which the soil 

 presents. 



M. Maxima Cornu, as a result of his observations, has 

 come to a conclusion contrary to the most commonly 

 accepted theory of the cause of the disease of the vine, 

 which attributes it to the absorption of the sap by the 

 insect, and holds that the Phylloxera does not divert the 

 sap to its own body, basing his conviction on his observa- 

 tions as to the length of the portion of the sucker buried 

 in (he rootlet compared with the thickness of the bark. 

 He considers that what the Phylloxera really feeds on is 

 the contents of the cellules of the bark, and perhaps of the 

 cambium layer. An exaggerated power of absorption has, in 

 his view, been attributed to the Phylloxera, and it would 

 rather seem that the flagging and ultimate decay of the 

 vine arises, not from the absorption of the nutritive 

 elements by the insect, but from the formation of new 

 tissues, which divert them from their proper end to nourish 

 abnormal growths. These new tissues or swellings 

 ijcnjlciiu'iits) of the roots are probably caused by an 

 irritation of the cambium layer, the result of which is the 

 hypertrophy of the excited part, while the formation of 

 the swellings brings about the death of the rootlets, and 

 through them the general decay of the vine. A natural 

 conclusion from these observations is that the health of 

 the vine may be improved by any means tending either to 

 produce fresh rootlets or to increase the absorption of 

 nutritive elements by those already in existence, though 

 the only true and radical remedy is to kill or drive away 

 the Phylloxera itself. 



When a vine is first attacked by the Pliylloxera, a 

 change occurs in the external appearance of the rootlets, 

 which, instead of being nearly cylindrical, exhibit the 

 swellings we have just mentioned of different shapes, 

 which are the first symptoms of the disease. The 

 Phylloxeras may often be seen on their surface. These 

 swellings are hard, and of a greenish or yellowish, or 

 sometimes of a deeper-coloured tint, according to that of 

 the external coat of the root when they are lull of sap, 

 but when they rot they become black and flabby, and 

 eventually dry up altogether. 



It is interesting to examine and compare in the same 

 root the structure of the part above the swellings with 

 that of the swelling itself, as by these means one can 

 come to a definite opinion, by comparing the diseased 

 with the healthy part, as to what are the new elements 



which are developed, and what are the characteristics of 

 the altered parts. By making a transverse section above 

 a sweUing in the vine, the structure is found to be that 

 of a normal root-shoot ; and, with the aid of a microscope 

 magnifying 60 diameters, the following appearances may 

 be observed : — (i) On the outside the external coat 

 {cojiclte subcrciise) composed of flattened cells, arranged 

 in rows and brown on the outer side : this tissue peals off 

 in layei's of a brown colour, and it is this that gives the 

 rootlets the yellow or brown tint they show according to 

 its thickness. (2) The cortical parench)ma, composed of 

 polygonal cells, full of starch, some of which, larger than 

 the rest, scattered about here and there, contain bundles 

 of raphides, long crystals parallel to each other. These 

 two constitute the cortical coat. (3) The woody portion, 

 composed of fibres and vessels, occupies the centre, and 

 is divided into three, four, or five woody sectors, and 

 between each two of these is a medullary ray — there is no 

 definite pith. (4) Embracing the woody tissue and in 

 contact with the cortical coat is the cambium layer, the 

 flattened cells of which, with their thin walls, full of a 

 thick plasma and always destitute of starch, form on the 

 one side the cortical and on the other the woody 

 tissue. The general contour of the section is circular. 

 To turn to the swellings. — The increase in diameter is 

 due to the formation of new elements, partly cortical, 

 partly woody, the cortical parenchyma becoming much 

 thicker, but otherwise resembUng the healthy tissue. It 

 is different with the woody tissue : the woody rays assume 

 very irregular outlines, and swell in all directions unevenly 

 beyond the limit of the single concentric circle which 

 terminates them with its circumference, in the healthy 

 state. The development of the cambium layer is also 

 abnormally increased, and there seem to be no vessels in 

 the new wood formed under these conditions. 



This altogether anomalous anatomical constitution is 

 in itself a refutation of those who even now hold that the 

 swellings are the result of normal growth. They really 

 are a purely local hypertrophy produced by the direct 

 action of the parasite. 



It is of great importance to the discussion of possible 

 means of extirpating the new insect, to investigate the 

 method it employs in getting from place to place and so 

 spreading its ravages. Putting aside as obvious the 

 movements of the winged variety, which, as we have said, 

 seems to be borne to fresh spheres of mischief by the wind 

 without any direct effort of flight on its own part, we come 

 to the wingless insect. Observation shows that the wing- 

 less Phylloxera progresses both along the surface of the 

 earth and follows also the line of the roots or the fissures 

 of a crumbly or broken soil. And first, to deal with the 

 surface-movements of the insect, they appear to be 

 extraordinar)' occurrences, the results of the concourse of 

 altogether special circumstances, for the exposure to the 

 air and to the sun's rays is very unfavourable to the 

 Phylloxera, which in the dry air dies of desiccation, 

 as may be easily shown by leaving exposed a root 

 covered with Phylloxera. It would seem, therefore, and 

 observation supports this idea, that the reason of the 

 surface-movements of the insect lies in the fact that in 

 getting from vine to vine, or sometimes from rootlet to 

 rootlet, it encounters obstacles which, not being a 

 burrowing insect, it cannot overcome, and therefore from 

 unwelcome necessity it has to mount to the surface, though 

 only to bury itself again when the next fissure shows 

 itself, leading to a fresh and unattached part. With 

 respect to the movements of the parasite underground, 

 some elaborate observations have been made by M. 

 Duclaux, and it is worth while to examine his results. If 

 one were to ask himself, a priori, which kind of soil 

 among those that prevail in the south-east of France 

 offers the greatest difficulty to the movements of the 

 Phylloxera, the answer which would inevitably suggest 

 itself would be that the sandy varieties are the least per- 



