ARTIFICIALLY SPREADING FUNGOUS DISEASES. 55 



gave only the slifjhtest trace of an infection or none at all, while the 

 second shakinjjj in four clilferent exi)eriments gave 20, 70, 4, and 

 less than 1 per cent as much infection as the first shaking. The 

 second shaking is, therefore, very unreliable as compared with the 

 first. These field experiments have been supplemented by a micro- 

 scopic examination of spore solutions. 



Two hundred red Aschersonia pustules freshly ])icke(l in Januaiy 

 were shaken ilve minutes in 1 ([uart of water, the solutioji })0ured into 

 a clean dish, and the same pustules shaken again in a similar way 

 three times. The solutions of the successive shakings were likewise 

 poured into separate dishes. Each solution, in turn, was thoroughly 

 stirred and the number of spores present in one-tenth cubic centi- 

 meter of solution (a veiy small drop) were counted by means of a 

 slide marked into one-tenth square millimeters. The count gave the 

 approximate numbers of spores in the successive solutions to be 9,188, 

 2,100, 274, and 19, respectively; or 79.3, 18.1, 2.4, and 0.2 per cent, 

 respectively. 



Effect of copj,er sprayers on mtality of spores. — It is a well-estab- 

 lished fact that fungi are susceptible to the effects of solutions contain- 

 ing very small quantities of copper. Consequently, in purchasing 

 spray pumps or retainers of any kind for work with white-fly fungi, 

 it has been considered advisable on general principles to avoid 

 copper and brass parts as far as possible. Numerous experiments 

 have conclusively shown that equally good infections can be secured 

 whether a copper or a galvanizcd-iron knapsack sprayer is used, 

 provided the spore solution is not permitted to remain in the tank 

 longer than is necessary to spray it into the trees. Throughout the 

 summer of 1908 the authors used a copper and a galvanized tank in 

 numerous duplicate experiments on difTerent occasions, including 

 nearly a thousand trees, and in all these no difference in infection 

 secured could be detected. As good infections were secured when 

 the copper tank was used as when the spore mixture was applied by 

 means of a ban(4 ])ump, and as good as resulted in check experiments 

 using the dipping and brushing methods where the spore solution was 

 carried in a wooden bucket. I^nsprayed trees developed no fungus 

 except where the natural spread was rapid. 



Effect of nutrients added to water mixtures of spores. — Experiments 

 to determine what benefits, if any, accrue from the addition of nutri- 

 ents to the ordinaiy water solutions of spores were begiui in 1906, 

 and were continued throughout 1907 and 1908. Agar, glucose-agar, 

 glucose, and gelatiji. were used in vaiying amounts, and the solution 

 allowed to stand varying lengths of time before application. As 

 Prof. Fawcctt has found a 5.10 per cent glucose-agar solution the best 

 medium for the germmation of the spores of the i-ed Aschersonia, and 

 that germination usually takes place in a little over 24 hours, field 



