DIVISION OF BOTANY 837 



SESSIONAL PAPER No. 16 



orchards it seemed likely that a goodlj- number of trees would be girdled and killed, 

 but in most cases it seemed as though a branch might continue to fruit for many years 

 after being invaded, cankers being found with successive annual growths of ten years 

 or more. In these neighbourhoods also, where orchards were well cared for, especially 

 in the matter of spraying, the disease did not appear to be destru<itive. Perithecia 

 were found in considerable quantity. 



" Around Kentville, Wolfville, Starr's Point, and other points in the upper ^xu- 

 napolis valley the orcharding is of a much better type- and while cankers could be 

 fo\ind, the amount of injury being done by them did not seem to be very great. In 

 this region also the most susceptible vaiiety, the Nonpareil, is grown to a less extent. 

 Altogether it seems clear that the disease is only a menace where proper pruning and 

 spraying are neglected. 



" On the return journey a visit was paid to Dalhousie on Chaleur bay. This is 

 apparently a very exposed point and the few apple trees noticed were very poor, 

 stunted, and apparently much injured by climatic conditions, Here one case of 

 Nectria ditissima on an apple tree was found." 



Silver Leaf of Fruit Trees. — Investigations of this obscure trouble carried on 

 since 1909, while successful so far as to prove that the peculiar silvering of the leaves 

 may in many cases be attributed to an infection with the fungus Sterev/m purpurenm 

 Pers. for which we have conclusive evidence, leave no doubt in our minds that this 

 curious phenomenon may result from other agents too. 



The fungus Stereum causes the leaves to assume the silvery colour, apparently by 

 the action of some ferment produced by the fungus, and the effect is prominently vi- 

 sible in the leaves ; it is in this case not due to a local infection but rather an action 

 at a distance. 



We have been able to make some observations in an orchard at Salmon Arm, B.C., 

 which proved the silvering of the leaves may also be due to a local agent, i.e., acting 

 directly upon the cells of the leaves and producing the silvery colour. 



In the fall of 1912 we observed a pear tree in the locality referred to, the leaves 

 of which showed typical silvering; the tree was marked for observation and was visited 

 again a year later after a request by the owner, who claimed he had succeeded in con- 

 trolling the disease by a simple application of Black Leaf 40, a nicotine preparation 

 now in common use against various insects. That the claims of the owner were cor- 

 rect was revealed by a more careful examination. The leaves covered by the spray were 

 nominally green, but those above the reach of the spray still showed signs of silvering. 

 This phenomenon was now carefully examined, when it was found that the appearance 

 of these silvered leaves differed somewhat from the Stereum silver leaf inasmuch as 

 the leaf was covered with clearly defined patches of silvery area, which in some 

 instances had become confluent, involving the whole upper surface of the leaves. This 

 is never the case in Stereum silver leaf. Examination of the surface with a 20-diam. 

 magnifying lens then revealed the presence of minute mites, apparently of the genus 

 Eriophyes. No determination was made at that time of the mite, but immediately a 

 thorough inspection of the leaves of other trees affected with silver leaf was made, 

 with the striking result that a mite of the same kind, or closely related at any rate, 

 was discovered. This observation no doubt accounts to some extent for the " recovery " 

 of trees from " silver leaf " which we have not observed in the " Sdereum " silver leaf. 



In order to show the close resemblance and difficulty of distinguishing these two 

 types of silver leaf, we forwarded specimens of true silver leaf and mite silver leaf to- 

 Mr. Brooks, of Cambridge, England, who is very familiar wit-h this disease. On receipt 

 of his report we found he was able to confirm our first diagnosis merely stating that 

 the specimens should be regarded as affected by silver leaf disease. On specially point- 

 ino- ^'^ +'■•0 differences this observer immediately was in a position to distinguish 



between them. 



From this preliminary stntement it will be seen that two very different causes 

 may at times result in producing very similar symptoms. 



Ottawa, 



