CHAP, xin.] Fungoid Diseases of Trees 285 



apothecia are developed in May ; but they can only burst when 

 favoured by long-continuous rain. Hard winters and dry 

 spring weather therefore tend to prevent the spread of the 

 disease. This disorder is of very frequent occurrence in 

 nurseries and young plantations. 



In Germany thirty years ago this disease of the Scots Pine 

 was merely ' an interesting observation,' but now it has practi- 

 cally become a widespread calamity *. Similar appearances of 

 leaf-shedding in the Pine may, however, easily be occasioned by 

 other causes. Although R. Hartig and Prantl have shown it to 

 be due to H. pinastri in a great many cases, Ebermayer has 

 proved that it can be caused by a process of drying up or 

 exhaustion owing to excessive transpiration in early spring ; 

 whilst Alers and Nordlinger proved that it was frequently due 

 to autumn frosts in rapid contrast with sunny days owing to 

 strong radiation of warmth from unprotected soils, more 

 especially after wet, cold summers unfavourable to the 

 hardening of the shoots. 



This disease attacks Scots Pine chiefly, and also the Austrian 

 Pine, between the ages of one to five years, although it is like- 

 wise found on plants up to about twenty years of age. Damp, 

 misty localities favour its spread, hence it is more frequently 

 found in plains and valleys, than in hill-side woods. The 

 best measures adoptable to prevent its spread consist in the 

 admixture of Spruce with the Pine, in the avoidance of delay 

 in pricking out seedlings in the nursery beds, in the formation 

 of Pine nurseries in places free from infection amid broad- 

 leaved woods if possible, and in the burning of all plants 

 infected. 



Some similar disorders are occasioned by H, macrosporum 

 on the two-year-old foliage of Spruce plantations from ten to 

 thirty years of age, and by H. nervisequium on two-year-old 

 and older foliage of Silver Fir. 



1 See Chapter VI. p. 130. 



