SUBMEESION OF FIELD AND FOEEST. 25 



trees : Hylesinus ater, F, ; H. oi)acus, Er. ; H. angudatus, Hb. ; H. 

 cunicularius, Kn. The sawflies, very injurious to coniferae, because their 

 larvse not only attack the adult needles but prefer to devour the young 

 shoots : Lyda campestris, L., and L. jyratensis, L., the larvae of which 

 bury themselves in August in the moss at the foot of trees to pass the 

 winter there. L. erytlirocejihala, L. (red-headed Lyda), the larvae of 

 which hide at the foot of trees in the month of June. Lo-plmjrus Pini, 

 the larvae of the second generation metamorphose into grubs in the 

 humus of the forest after passing the winter there. Gryllotalpa 

 vulgaris, Latr. (mole cricket). Winter submersion has little action 

 on it, because like the white worm it descends deeply into the ground 

 at the approach of cold. The following Lepidoptera : Lasiocamjna 

 Pini (or bombyx of the pine), the grub of which hibernates as chrysalis 

 in moss at foot of ti-ee. Trachea jnnipercla and Fidonia piniari, L., 

 both hibernating in ground in the state of chrysalis. Submersion also 

 frees the forest from the rodents which undermine it, and which in 

 winter nibble the bark of young trees. But if on the plain the 

 difficulties of submersion are not great, on the slopes where it is 

 necessary to trace a series of parallel channels which flood the ground, 

 by overflowing, this method becomes very costly, especially if it is 

 necessary to raise the water by means of turbines or pumps. 



Antiphylloxeric Submersion. — In the beginning of the phyllo- 

 xeric invasion in 1868, the sands of the dunes (sandhills) were found to 

 be unfavourable to the propagation of this dangerous homoptera. The 

 fact was observed at Aigues-Mortes, where vines planted in the dunes 

 remained flourishing, whilst those planted in the neighbourhood died 

 without exception. According to Foex the sands exhibited a certain 

 immunity to the phylloxera when they contained at least 80 per cent 

 of silica, but a small amount of clay or limestone sufficed to deprive 

 the soil of this precious property. This immunity, studied by Van- 

 nuccin at the viticulture laboratory of Montpellier, would appear to 

 be due to the asphyxia produced by the water retained by capillarity 

 between the grains of sand. Is that water sufficient to cause the 

 asphyxia of the insect ; is it not rather the physical constitution of 

 the sand which hinders the passage of this insect from one stock to 

 another? That is a point which has not yet been proven. Balbiani 

 disputes the theory of the asphyxiant action of water in permeable 

 ground consisting almost exclusively of silica ; he has in fact caused 

 young phylloxera which he had hatched in a sand medium to live 

 under water for fifteen days. On the other hand, Faucon has observed 

 that it takes forty-five days' immersion in water to kill the phylloxera. 

 Now, sands are never impregnated so long by rain-water. Be that 

 as it may, it was this immunity of the sands which gave the idea of 

 submersion for the destruction of the phylloxera. It had formerly 

 been remarked that long-continued rain w^as unfavourable to it, and 

 that it shunned moisture by burying itself in the soil at great dej^ths, 

 only dying when the soil was thoroughly soaked. Eminent vine- 

 growers, Faucon and P. Castelnau, concluded that submersion might 

 be efficient, and since 1870 have submitted a part of their vines to 

 this treatment. The results obtained were surprising. The following 



