Sept. 1895.] 



INJURIOUS INSECTS AND FUNGI. 



179 



Tn connexion with this inquiry, Dr. Voelcker reported in 1894 

 upon experiments made by himself, and, after giving the particu- 

 lars of the analyses of several soils, stated as follows : " If these 

 analyses are compared it will be seen that the only strongly 

 marked points of difference, as between soils liable to disease 

 and those not liable, are in the relative proportions of lime 

 contained and to a lesser extent in the potash. The latter may 

 have something to do with the question, but this is not made 

 clear by the analyses, the 14 per cent, of potash in No. 1 being 

 practically the same as the 11 per cent, in Nos. 5 and 6. But 

 the difference in the amounts of lime contained in the soils of 

 either class are very striking, and clearly point to this feature 

 of the presence or the absence of sufficient lime being intimately 

 associated with the freedom from, or liability to, disease. All 

 the soils on which ' finger and toe ' never occurs are those which 

 an agricultural chemist would describe as containing sufficient 

 lime ; all those which are subject to disease are those recognised 

 as being deficient. As regards the actual per-centage of lime 

 required, it would appear that the presence of "75 per cent, of 

 carbonate of lime is enough to constitute a soil ' disease proof,' 

 if, indeed, such a condition of soil can exist ; while less than one 

 half per cent, of carbonate of lime would seem insufiicient to 

 ward off the attacks of the fungus." Dr. Yoelcker adds : " In 

 saying this I am aware that it has not been shown that the 

 fungus cannot thrive in a soil which contains three quarters of 

 one per cent., or even more, of carbonate of lime ; but the 

 analyses I have set out show that none of the soils which are 

 reported to be unaffected by disease have less lime than the 

 first-named per-centage, and there is strong ground for conclud- 

 ing that in this lies the determining factor. For this reason I 

 am of opinion that further inquiry should take the form of 

 ascertaining whether it is possible to infect with the fungus 

 land that is rich in lime, or whether the presence in the soil of 

 lime in sufficiency has a. destructive or retarding effect upon the 

 vitality and spread of the fungus." Dr. Soraerville has shown 

 in the results of his experiments, given in the December number 

 of the Royal Agricultural Society's Journal for 1894, that the 

 application of lime to soil infected with Plasmodiophora pre- 

 vented the spread of the fungus in proportion to the amount of 

 lime employed. In one instance, a dressing of only 700 lbs. of 

 very finely ground quicklime per acre nearly cured the disease 

 in land that was infected. As Dr. Somerville points out, the 

 experiment was made upon a small plot, and this small quantity 

 of lime per acre would probably not prove so effective in ordinary 

 field cultivation. But he goes on to say that by grinding the 

 lime to an impalpable powder in the manner adopted in his 

 experiments its spreading and mixing power is vastly increased ; 

 and that farmers who sow 5 cwt. per acre, as was done in some 

 of the field experiments, maintained that the visible e:ffects, so 

 far as whitening the land was concerned, were as great as when 

 5 tons are applied in the usual way. The cost of grinding is 



