F. T. Brooks and M. A. Bailey 207 



of the silvered bushes), horse chestnut, Philadelphus, and in gooseberry 

 bushes by using mycelium grown in pure culture, although with these 

 plants (cherry trees excepted) the percentage of successful inoculations 

 was much less than in plum trees. Where inoculation was followed by 

 silvering it was found that the fungus made considerable progress in 

 the tissues, but in the unsuccessful inoculations the fungus grew very 

 little. In 1913 certain inoculations of young cherry trees were described 

 and it was pointed out (2) that the small branches experimented with 

 were usually killed outright without an opportunity for silvering to be- 

 come manifest, but in the successful inoculations now mentioned older 

 branches were used for the experiments with the result that several 

 became silvered. 



On the other hand, the following plants have been inoculated with 

 Stereuni. purpureum without silvering resulting : black currant, beech, elm, 

 sycamore, cherry laurel and Portugal laurel. As regards the laurels, 

 other species, e.g. S. rugosum and S. spadiceum, have also been used 

 as the inoculant, but without success. All these plants, on several of 

 which silvering has been occasionally seen in nature, were young and 

 of vigorous growth and possibly therefore particularly resistant to in- 

 vasion by the fungus. Inoculated branches which were examined showed 

 that the fungus had made little advance in the tissues. 



4. ATTEMPTS TO INDUCE SILVERING OF FOLIAGE OTHER THAN 

 BY INOCULATION WITH STEREUM PURPUREUM. 



Various attempts have been made to induce silver-leaf in plums 

 without the intermediary of Stereuni purpureum, and although these 

 have given generally negative results some are worthy of mention. 



Attention was first directed to the possibiHty of inducing silver-leaf 

 by injecting into the woody parts of healthy Victoria plums a sterile 

 extract of wood known to be attacked by Stereum. purpureum, the 

 assumption being that the extract would be carried up to the leaves by 

 the transpiration current where it might cause silvering. The extract was 

 rendered sterile, except for the minutest viruses, by filtering it through 

 a Chamberland bougie. The injection was carried out in the field by 

 two different methods: 



[a) In the lower part of the main stem by boring a hole, in which 

 a cork traversed by a glass tube was placed, the latter being connected 

 by rubber tubing to a reservoir situated three to four feet above and 

 containing the extract. The joints were sealed with plasticine and air 

 was excluded from passing into the stem. 



14^2 



