A Cucumber Leaf Disease. 



167 



strong heat (and often grown in a soil, one part out of three of 

 which is stable manure) are rendered " susceptible" to the attacks 

 of fungi through the production of soft, rank, sappy growth, and 

 are often weakened in their constitution. 



It is true that the ordinary method of cultivation may 

 appear to give the best returns, and that cucumbers have been 

 grown thus for years with great success ; but it must be remem- 

 bered that it offers two conditions which tend to induce a fungus 

 to become parasitic, namely, the providing of congenial sur- 

 roundings and rendering the host plant susceptible to the 

 attack. 



Within the last seven years the cucumber has been attacked 

 by two new leaf parasites, and unless these can be stamped out, 

 or held in check by some means, the present method of culture 

 may have to be altogether modified. 



It seems very likely that Dendryphium was introduced into 

 the cucumber houses by the manure that was used, and from 

 thence spread to the cucumber plants. As before mentioned, 

 it attacks the leaves, and generally forms small pale spots, 

 which gradually increase in size, but are quite distinct from the 

 blotches produced by Cercospora. The dead tissue of the 

 spots often falls out, so that the leaves appear as it injured 

 by the " shot-hole fungus." In bad cases, however, the fungus 

 spreads considerably in the leaf tissue, and it may destroy 

 all of it except the larger veins. When quite young 

 leaves are attacked the vascular bundles may be also partly 

 destroyed and curious malformations ensue. Spotting also 

 occurs on the old leaves, and though the damage done to them 

 is not generally quite so severe as in the younger ones, the 

 destruction of leaf tissue is always serious to the welfare of the 

 plants, In very bad cases the young shoots and fruits are 

 utterly ruined by the fungus. 



On examination of the spots with a pocket-lens a soft, velvety 

 growth may be seen, though this may not be visible the first day 

 the spots appear. The fungus, when once it has obtained an 

 entrance into the plant, grows vigorously in the tissues, and after 

 about two days the conidiophores (or spore-bearing hyphae) 

 break through the epidermis and give the velvety appearance 

 just alluded to. 



