FUNGI 247 



factors in hastening the dying down of the haulms, and the 

 ripening of the tubers. 1 



That spraying can destroy all the spores on the leaves, and 

 render the plant quite free from disease, is amply disproved by 

 all the results obtained; and, where disease is present, two 

 effects are produced (apart from any possible toxic action of the 

 copper on the potato plant itself alluded to on p. 244) ; on the 

 one hand, the fungoid growth is partially destroyed, but on the 

 other, the haulms are thereby rendered more vigorous and 

 succulent, and they, consequently, present a readier passage for 

 the mycelium from such fungus spores as have not been destroyed. 



The percentage of diseased tubers can, therefore, be no measure 

 of the general result of the spraying, it is only one of the results, 

 and it may be that, as in the case just quoted, this percentage 

 is actually increased, even doubled, by the spraying. In the 

 same way, neither the increase in the total crop, nor even that 

 in the sound portion of the crop, can be taken as a true measure 

 of the results of the treatment, though the latter is, at any rate, 

 a practical measure, for the yield of sound tubers is the only one 

 which is of value to the grower. 



That disease is encouraged by the vigour of the plant, and 

 especially by the vigour and succulence of the haulm, may be 

 inferred from the large increase of disease noticed when dung, 

 instead of artificials, was used, although the total crop of tubers 

 was the same in the two cases (p. 245) ; and in that case, as was 

 seen, spraying produced no further increase in the vigour of the 

 haulms, and, consequently, no increase in the percentage of 

 tubers affected. 



That the effect of spraying, or of any other treatment benefiting 

 the plant generally, should be greater when the plants are in a 

 bad condition than when they are flourishing, is what naturally 

 would be expected, and hence the greater effect of spraying in 

 increasing a poor than a heavy crop. 



Two other points connected with potato disease were investi- 

 gated at Woburn : the one was the steeping of the seed in copper 

 sulphate solution of various strengths prior to its being sown. 

 The results were not satisfactory. When soaked for 10 minutes 

 in a i per cent, solution, there was no apparent benefit, the crop 

 of sound tubers being practically the same as with unsteeped 



1 Sprayed potatoes are generally about a fortnight later in ripening than 

 unsprayed ones. This, indeed, is one of the disadvantages attributed to 

 spraying, for the delay in ripening may not only cause inconvenience on 

 the farm, but may result in a certain amount of " growing out " of the 

 tubers. 



