HYSTERIACEAE 141 



the leaf, causing the asci to swell, and consequently rupture 

 the apothecium. 



' Diseased seedlings usually die, and do so with certainty 

 unless about half the number of leaves escape the parasite.' 



Preventive Means. — It is certainly not advisable to 

 plant diseased year-old seedlings, nor those of two years 

 old or more, as such rarely recover the effects of trans- 

 planting. 



If the mycelium of the fungus passes into the tissues, 

 and especially if the pith is browned, the plant is certain 

 to die almost at once. 



Seed-beds should not be exposed to the direction of 

 the prevailing wind, especially if it blows over a diseased 

 area, as spores are almost certain to be carried, and some 

 of these are almost as certain to be deposited on the seed- 

 lings. Neither should the beds be formed under older 

 pines, as such may possibly have some diseased leaves, and 

 the spores would be washed down by rain. Weymouth 

 pines are not attacked by this disease, and may take the 

 place of pines destroyed by the disease if conditions are 

 favourable for their growth. 



Goppert, Verhandl, d. schlesischen Forstvereins^ 1852, p. 67. 

 Hartig and Somerville, The Diseases of Trees (Engl, ed.), 

 p. no, fig. 



According to Hartig the silver fir also suffers from leaf- 

 cast, old trees even losing the majority of their leaves, 

 due to a fungus called Hysterium nerviseqiiiuf?i. The fruit 

 forms a black line on the midrib on the under surface of 

 the leaf. Another species of Hysterhim^ H, macrospornm. 

 sometimes destroys the leaves of the spruce. A brown 

 coloration indicates the presence of the mycelium of the 



