78 



Cause of Canker. 



True apple canker is caused through the infection of the tree by a parasite 

 fungus laiown as the canlier fungus (Ncctaria ditisfsima). The spores of this 

 fungus gain admission into the tissues of the tree through woun<ls which are 

 always to be found on fruit trees. Hence the fungus belongs to that group of 

 fungi which are often termed wound-parasites. Trees may have also what 

 may be called " false canker," where the effects resemble those of true canker, 

 but in them the nectaria fungus is not to be found. The cause of this " false 

 canker " has been attributed to bacteria, and the researches of Byrzezinski 

 seem to point to this conclusion. 



Prevention and Remedies. 



When young trees are attacked all affected liranclies should be carefully 

 cut off below- the point of infection and burnt. The exposed cut should then 

 be protected with a coating of ordinary gas-tar. When thick branches are 

 diseased the affected parts may be cut out and the cuts treated with tar. 



It is most important never to use scions from a tree that is or has been 

 disea.sed : through the neglect of this precaution thousands of .voung stoclc 

 have been ruined. Where trees have been neglected and are badly diseased 

 they should be cut down and burnt. 



Healthy and diseased trees should not be pruned with the same knife, as 

 spores are often carried from tree to tree during pruning, and the newly-cut 

 surfaces offer an admirable starting place for fresh infection. The tools 

 should be sterilised after pruning an infected tree. 



Spraying is of very little use in destroying this disease; still, lime-and- 

 sulphur mixture seems to lessen its ravages considerably. Prt)per cultural 

 methods, and the keeping of the trees in a vigorous state, will generally prove 

 successful in warding off this disease. — SeiL- Zealand Bulletin No. 10. 



GUMMOSIS 



Is the name given to a disease which attacks stone fruits, especially 

 sweet cherries. Its nature is not well understood, and is described in 

 Michigan Bulletin 25, as follows : — 



The flow of gum from branches of plum, peach, cherry, almond, etc., has 

 in some cases been attributed to the presence in the tissues of a parasitic 

 fungus. Thus Massee described a guuunosis of the ilowering almond due to 

 the attacks of Cladosporium epiphyllum, and a similar trouble on the same 

 plant has been noted by the writer under the head of Brown Rot of Plum 

 {Selerotinia fruetiijenn i. 



Cludosporinin. eitiphylluni has also been found causing gummosis on the 

 purple-leaved variety of the JMyrobalan plum, grown for ornament at the 

 Agricultural College, while the same disease on cultivated plums has been 

 found to be associated with a species of Cladosoporium. In many cases the 

 trouble probably begins in some crack or wound which allows the fungous 

 parasite to gain an entrance. The presence of the mycelium induces a flow 

 of sap which exudes and hardens, forming tear-like drops, sometimes of 

 considerable size. This gum is partl.v utilised by the fungus in the production 

 of more spores. The portion of branch beyond the affected spot may in some- 



