1 66 



A CUCUMBER LEAF DISEASE. 



Dendryphium comosum, Wallr. 



For the last four or five years growers of cucumbers have 

 suffered severely from the disease known as Leaf-blotch, caused 

 by the fungus Cercospora melonis. (See Board of Agriculture 

 Leaflet No. 76.) 



This season another form of leaf disease has been met with, 

 which, though rather similar in appearance to the Leaf-blotch, 

 is found to be caused by an entirely different fungus, viz., 

 Dendryphium comosnm, Wallr. 



This new disease was observed to appear as early in the 

 season as March, which is about two months earlier than the 

 time the ordinary Leaf-blotch disease first shows itself. It 

 attacks the plants when quite young, and by killing the tissues 

 of the leaf, causes small spots, which are easily detected ; in bad 

 cases the growing points of the shoots are also infected and 

 destroyed. 



The Dendryphium disease, as well as being interesting from a 

 scientific point of view, should prove a warning to growers, as it 

 affords an illustration of the way in which a disastrous epidemic 

 may originate. Dendryphium comosum is a fungus long known 

 to mycologists ; it occurs on decaying vegetable matter, but 

 always as a saprophyte, and there has never been any reason to 

 expect this fungus to become parasitic, rather than any other of 

 the numerous saprophytes with which we are familiar. It has 

 found, however, in the cucumber plant a host on which it can 

 readily flourish, at any rate under the conditions in which this 

 plant is usually grown. 



When these conditions are considered, it cannot occasion a 

 moment's surprise that the cucumber is the prey of parasitic 

 fungi. The warm, moisture-laden atmosphere of the forcing- 

 pits is ideal for the germination of fungus spores and the growth 

 of mycelium. The plants themselves, too, having been forced in 



