i9io.] 



A Disease of Fig Trees. 



47 



planted, and consequently was in a highly susceptible 

 condition. 



Infection of a potato tuber is only possible through the eye, 

 and then only when the sprout is quite young ; hence, when 

 the tubers were examined, all had passed the stage of possible 

 infection, and thus represented the percentage of immunity 

 due to "greening." 



There are two primary reasons why autumn "greening " of 

 potatoes prevents infection. For some unknown reason the 

 swarm-spores of species of Synchytrium * avoid entering cells 

 containing chlorophyll, and all the cells of autumn 

 "greened" potatoes are rich in chlorophyll. Again, the 

 exceedingly slow rate of growth of such sprouts results in 

 the formation of a comparatively thick cuticle and epidermis, 

 through which swarm-spores could not penetrate. 



In February of the present year the Board received from 

 Sussex specimens of diseased wood of fig trees. A consider- 

 able area of trees is affected. Examin- 

 A Disease of ation showed that the disease is due to 

 Fig Trees. the fungus Libertella ulcerata, Mass. 



In some respects it produces effects 

 similar to apple canker (Nectria ditissima, Tul.), described in 

 Leaflet No. 56, and it might perhaps fittingly be named "Fig 

 canker." 



The fungus causes the branch or twig to crack slightly 

 (see illustration), but does not produce the gaping wounds 

 which are caused by apple canker. The wood becomes ashy 

 grey in colour, enabling the diseased wood to be easily distin- 

 guished. In badly affected branches all parts above the 

 canker die. In twigs of recent growth the grey colour is 

 not evident, but the twigs die back from the tip. Old trees 

 were found to be much more badly diseased than young ones, 

 and in some cases canker spots could be seen quite close to 

 the ground on the main branches. The fungus appears to 

 obtain access to the wood through wounds due to various 



* The fungus causing Wart Disease or " Black Scab " of Potatoes will in future 

 be known as Synchytrium endobioticum Percival, and not as ChiysophZyctis endobiotica 

 Schilb. as heretofore. 



