PLANT DISEASES. 77 



normal reflection of light from the leaf and giving the latter a 

 silvered appearance. Once inside the tree, the fungus spreads 

 upwards and downwards, chiefly in the wood, and sooner or 

 , later the branches begin to die off. In the majority of cases the 

 fungus spreads extensively, often causing the death of the tree; 

 and fruit bodies of the fungus arising on the dead branches are a 

 potent source of infection to healthy trees in the immediate 

 vicinity. By careful and prolonged experimental work it has 

 been proved that if the fungus is prevented from fruiting within 

 a plantation the spread of the disease is greatly reduced. As a 

 result of the work the Silver Leaf Order was recently introduced 

 by the Ministry of Agriculture and Fisheries under the Destruc- 

 tive Insects and Pests Acts. Under this Order, fruit-growers 

 must take adequate measures to prevent the fungus from fruiting 

 in their plantations; for example, all dead wood, on which the 

 fungus can fruit, must be cut away and destroyed. Fruit- 

 growers have welcomed the Order and are prepared to co-operate 

 to the utmost extent required. 



During the past year considerable attention has been paid 

 to silver leaf disease in apples and peaches, in both of which it 

 is becoming increasingly serious. In these fruit trees the disease 

 has been found to be due to the same fungus as in plums, and 

 to take the same course. The varieties of apples commonly 

 affected are Early Victoria, Lord Grosvenor, Lord Suffleld and 

 Newton Wonder. In an apple plantation of about six acres 

 near Wisbech more than i,ooo trees were found to be silvered 

 in all stages of attack, the epidemic being due to large branches 

 within 2 feet of the ground having recently been cut carelessly 

 to facilitate cultivation and the wounds not protected, thus 

 affording opportunity for the fungus to enter. The disease is 

 prevalent on peach trees in glasshouses on the south coast. 

 Work has been commenced at Cambridge and East Mailing 

 on the susceptibility to silver-leaf of the various stocks used for 

 plums, and of the relative susceptibility of common varieties 

 worked on different stocks. Experiments are also in progress 

 at East Mailing to test the effect of working stocks at different 

 levels, also the effect of alternative methods of stooUng and 

 budding with a view to reducing the possibility of infection 

 during these operations. A good deal of preliminary work has 

 been done in attempting to cure the disease by injecting some 

 substance which will kill the fungus without injuring the tree 

 At the same time laboratory experiments are in progress to test 

 the effect of these substances on the fungus grown artificially, 

 Some experiments have also been made as to the possibility 

 of curing light attacks by ring-barking. Research is also in 



