TRANSACTIONS OF SECTION K. 489 



Bordeaux mixture is used on them, at the lowest concentration at which it is 

 efficacious as a fungicide, their leaves are affected to the extent that they 

 drop off, while on other varieties of apples Bordeaux mixture at double the 

 concentration can be used Avithout causing injury. A remarkable case of injury 

 caused by the vapour rising from solutions of soluble sulphides is observed 

 with the variety of gooseberry called Yellow Rough. A lime-sulphur wash at 

 a concentration which causes no injury when sprayed on the leaves of other 

 varieties of gooseberry causes almost complete defoliation when sprayed on the 

 leaves of Yellow Rough, or even when sprayed on adjoining bushes, or on the 

 ground under the bush. Whether this susceptibility is correlated with any 

 morphological characters, or is due to specific differences in protoplasmic 

 reactions of the cells, are questions which should be answered by the botanist, 

 and will give valuable help in solving the problem of the efficient spraying 

 of the manifold varieties of cultivated plants. 



The problem presented to the chemist is obviously that of finding materials 

 which are able to cause death to the fungus without causing injury to the host- 

 plant — a problem which is based upon knowledge of the behaviour towards 

 plant tissue of different chemical substances. Much remains to be done in the 

 direction of acciimulating such information, and it is felt that some systematic 

 work should be undertaken to ascertain what are the effects produced by 

 different types of chemical substance, such as oxidising agents, colloidal 

 substances, hormones, &c., towards living plant tissue. 



With information of this kind it may be possible to classify chemical 

 substances which have fungicidal properties according to the degree of intensity 

 of their action in this respect and, also, with regard to their behaviour towards 

 the host-plant. 



The results which have been obtained from work of this kind in the case 

 of copper fungicides are of sufficient importance to justify such work being 

 largely extended. It is only by careful systematic study that the mode of 

 action of fungicidal substances will become known. It will be necessary in 

 this connection to study not only behaviour of a substance itself towards the 

 fungus and towards the host-plant, but also the behaviour of substances which 

 are closely related to it. For example, when, investigating the mode of action 

 of soluble sulphide spray fluids, it is necessary to carry out trials not only 

 with different sulphides of the same element, but also with the corresponding 

 sulphides of similar elements, because, by so doing, the particular action or 

 activity may be observed to be toned down or otherwise modified so that the 

 mode of action may become detectable. 



Another aspect of the problem under discussion, and an important one, is 

 the examination, of the part played by certain attendant substances, not of 

 themselves possessing recognisable fungicidal properties, but which cause the 

 fungicidal property of another substance with which they are intimately mixed 

 or in solution to become much more marked. It is thought probable that an 

 instance of this kind is to be found in the case of paraffin, which when present 

 in small quantity appears to increase the fungicidal intensity of a soluble 

 sulphide spray fluid. Another case of a similar character is that where an 

 increase in the concentration of soap renders solutions of liver-of-sulphur 

 fungicidal. The importance of gaining information as to the behaviour of 

 attendant substances towards the host-plant as well as towards the fungus will 

 be obvious in view of the desirability for combining insecticides with fungi- 

 cidal washes, the insecticide, from this point of view, being regarded as the 

 attendant substance. 



In the class of active sprays it is of paramount importance that the fungi- 

 cide chosen should be brought into intimate contact with the fungus, and when 

 this presents a surface which is difficult to wet owing to the presence of air 

 films, some substance has to be added which will lower the surface tension 

 of the fluid. It seems highly desirable that some reliable method should be 

 devised for testing the wetting power of different spray fluids, and that a 

 careful study of this problem be made. 



