4 2 SECOND REPORT ON ECONOMIC BIOLOGY. 



this. There is undoubtedly some predisposing conditions where trees, 

 especially plums, are planted too deep or on stiff soil with a cold clay 

 beneath. 



Wherever trees are found to be attacked they should at once be 

 sprayed with a mixture of lime and soft soap to prevent the spores 

 being blown therefrom, and then cut down and burned. 



In purchasing new stock very careful examination should be made 

 to see that there are no signs of the disease, or better still, a guarantee 

 should be obtained that the disease had not occurred in the nurseries 

 or orchards in which the young trees have been grown. 



BEECH SEEDLING MILDEW. 



Phytophthora omnivora, De Bary. 



This is a well-known disease, and one that in wet years proves 

 very destructive. In addition to the seedlings of the beech, those of 

 ash, maple, robinia, Scots pine, spruce, sycamore, etc., are liable to 

 attack. 



The disease may attack the seedlings in their earliest stages 

 before appearing above the surface of the ground, or appear as spots 

 or dark-coloured blotches on the cotyledons, or on the primary leaves. 

 If the cotyledons only are attacked, and the weather is dry, the plants 

 may recover, but where the attack is more extended, and particularly 

 so in damp weather, the disease spreads to the stem below the 

 cotyledons and the plants rapidly decompose. In dry weather they 

 wither up, assuming a scorched appearance. 



In coniferous plants the roots frequently decay before the seedlings 

 have reached the surface. 



The disease is highly infectious and spreads rapidly, particularly 

 so in damp warm weather, and where the seedlings are shaded by 

 trees or artificial coverings of any kind. 



The spores (oospores) lie dormant in the soil during the winter, 

 infecting the germinating seedlings in the spring. Hartig 1 states 

 that they may retain their vitality for four years. In the beech 

 the mycelium of the fungus spreads into the tissues of the cotyledons 

 and stem, hyphae then make their way through the epidermis and 

 form sporangia ; these when ripe drop off, and coming into contact 



iUnters. aus dem Forstbot. Inst., 1880, p. 33. 



