INJURIES INDUCED BY PLANTS 



109 



Later on the apothecia appear on the under side as a longi- 

 tudinal ridge on the mid-rib, and ripen in the following April, 

 when the shoot is three years old. A large proportion of the 

 leaves, however, fall earlier, the pcrithecia being produced on 



/ 



FIG. 52. The under side of a branch of 

 silver fir, showing the perithecia united 

 into a longitudinal ridge. 



FIG. 53. Hysteriuin ner- 

 ziisegttiuin on the leaf 

 of the silver fir ; the 

 leaf on the left shows 

 the apothecium on the 

 under side, that on the 

 right the spermogonium 

 on the upper side. 



the comparatively few leaves that remain in situ. It may also 

 be remarked that still older leaves may contract the disease. 



HYSTERIUM MACROSPORUM 1 



This disease of the spruce produces the " spruce-leaf redness," 

 which in many years occurs with great severity in woods from 

 ten to forty years old. 



Its presence may be detected by the leaves of the previous 

 year's shoots turning brown in May, or possibly not till autumn, 

 and by the invariable occurrence of abundant mycelia in the 

 leaves even before they become brown. Leaves which change 

 colour in spring reveal the commencement of the formation of 

 perithecia in July of the same year, and these ripen next spring 

 in April and May. At that time they are present on the two- 

 year-old shoots. I observed this rapid process of development 

 in the humid climate of the Erzgebirge. At Eberswalde, on the 

 other hand, the leaves on the two-year-old shoots do not become 



1 R. Hartig, Wichtige Krankheiten, p. 101. 



