245 



Number of Sucker. 



1. 



3. 



4. 



5. 



Total length of sucker from its point of 



origin 



Height reached by the discoloration 



visible to the naked eye 

 Height reached by the hyphae 



cm. 



110 



cm. 

 140 



cm. 



102 



cm. 



80 



65 



83 



52 



51 



62 



79 



51 



47 



cm 

 95 



60 



■> 



For some little distance above the point where the brown 

 streaks cease to be visible to the naked eye the microscope shows 

 scattered patches of brownish material in the vessels. 



In completely silvered trees and in those where the lowest set 

 of branches (the first branches developed on the stem) were 



infected the discoloration was continuous 



from the twigs 



into 



the branches, down the main stem, through the point of union 

 between scion and stock, into the superficial roots of the latter, 

 and from these roots it could be traced again upwards into the 

 stem of the sucker. 



In agreement with previous workers, I found that no trace of 

 hyphae could be observed in the leaves or petioles of silvered 

 plum trees and suckers. Hand-sections made from the dis- 

 colored zone of the root stock, branches and twigs, and of the 

 roots and stems of suckers, disclosed the exceedingly minute 

 hyphae which, when stained, could be seen invading the wood 

 vessels in all directions. In suckers the fine hyphae extend 



from the cambial 



region inwards 



into the wood parenchyma; 



they sometimes keep a straight course in the discoloured vessels, 

 but occasionally branch when a few filaments may trespass upon 

 the yellowish-brown deposit of the cell-cavity. The hyphae do 

 not seem to enter a vessel at any particular spot, since they can 

 be seen passing across the lignified walls in their thickest parts, 

 and they develop luxuriantly in the lumen of the vessels. They 

 can also be traced in the intercellular spaces, as in Text fig. 1, 



Text fig. 1.— Longitudinal section through the wood of a silvered plum 



sucker, Brompton stock. 



in fact, wherever there is room for development. In the living 

 tissue no hyphae were found outside the cambial region ; but in 



