191 1.] Summary of Agricultural Experiments. 779 



Bordeaux mixture without excess of lime, the leaves brought some 

 copper into solution.. Care was taken to choose uninjured shoots, but 

 it is very difficult to find leaves quite free from small injuries. The 

 small amount of copper dissolved by exudations from these small 

 injuries increases the injuries, and these then proceed to dissolve more 

 copper. Experiments with single leaves supported this view, and 

 though the results are inconclusive as to the power of uninjured leaves 

 to exert a slight solvent action, the authors are inclined to attribute 

 the action rather to such injuries to the foliage. 



The question of the existence of a solvent action of the fungus itself 

 upon Bordeaux precipitates has hitherto not been settled. In this 

 investigation hanging drop cultures of spores were made with Bor- 

 deaux mixture and with the filtrate from it. In the filtrate germina- 

 tion and subsequent growth were fairly vigorous, while in the drops 

 of the Bordeaux mixture germination was rare. Diffusion tubes were 

 then used to separate Bordeaux precipitate from its filtrate, when the 

 spores germinated both in the filtrate outside the diffusion tubes and 

 in the diffusion tubes containing the precipitate, but in the latter case 

 only at a little distance from the precipitate itself. In the final experi- 

 ments films of Bordeaux precipitate were allowed to dry on cover-slips, 

 and films of Nectria conidia were superimposed on these films, over- 

 lapping them. After 24 hours in a moist atmosphere there was a 

 sharp limit between dead and living conidia which coincided practically 

 exactly with the edge of the copper film. Beyond the copper zone 

 nearly all the conidia were living, and had germinated in many cases, 

 especially in the region farthest removed from the copper. From these 

 results it is concluded that there is a solvent action on the part of the 

 fungus, which is, however, not strong enough to produce serious toxic 

 effect except when direct contact with particles of the insoluble copper 

 compound occurs. The action is purely local and cannot result in the 

 bringing into solution of sufficient copper to exercise a general fungi- 

 cidal action over the whole surface of a leaf. Some spores, e.g. 

 Puccinia spores, which have a thick resistant coat, may be uninjured 

 by contact with the copper compound, and growth will apparently be 

 possible if the germ tube escapes contact. As far as practical con- 

 siderations are concerned, this work would support the conclusions 

 arrived at by fruit-growers, viz., the necessity for thorough spraying, 

 so as to coat as completely as possible the surfaces liable to infection, 

 the importance of the finely divided form of the copper precipitate, 

 and of the adhesive properties of the spray. It explains also how 

 Bordeaux mixture may be effective immediately after application. 



Silver-Leaf Disease (Jour, of Agric. Science, Vol. IV., No. 2, Octo- 

 ber, 191 1). — In a paper on Silver-Leaf Disease, Mr. F. T. Brooks gives 

 an account of investigations carried out by him at Cambridge with 

 reference to this disease. The results confirm the conclusions of Prof. 

 Percival and Mr. Pickering (summarised in this Journal, vol. xviii., 

 p. 38) that the disease is caused by the fungus Stereum purpureum. 

 The author succeeded in producing the disease in healthy plum-trees by 

 inoculating with the spores of the fungus. He is of opinion that the 

 disease is probably communicated in this way from diseased to healthy 

 trees. Mr. Brooks's investigations have been aided by grants from 

 the Development Fund. 



