LARCH NEEDLE-CAST. 



469 



in their third year, or on older needles, but a large number of 

 the infected needles have generally fallen before this occurs. 



This disease is widespread in silver-fir forests, and has 

 proved destructive in the 

 Erzgebirge, where the 

 trees lose most of their 

 needles. 



Burn affected subjects. 



22. Sphaerella laricina, 



n. sp. 

 (Larch Needle-cast.) 



a. Description and mode of 

 Attack. 



Often in July, smaller or 

 larger brown specks appear 

 on larch needles, on which 

 later very small black 

 conidiophores project in 

 groups. From beneath 

 these, the colourless my- 

 celium, which is richly 



ramified, develops in the needles, partly in their intercellular 

 spaces, partly in the cells of their parenchyma. 



Inside the conidiophores, small hollows develop with very 

 fine basidia, at the ends of which are very small conidia. 

 These fall oft' and are carried away by wind, or washed out 

 by rain, and reach the young twigs of the tree, where, after 

 a few hours, they germinate and infect the needles. The 

 needle-cast thus increases progressively in intensity. By the 

 death of the twigs, the longitudinal growth of the affected 

 plants suffers, and owing to crowding by neighbouring trees, 

 they often die. The fall of sickly or dead needles commences 

 in July. 



On the needles that fall to the ground in the following 

 summer, globose, dark brown perithecia develop, which 

 spread the disease. The mycelium growing in the needles 

 becomes hard, thick walled, and is coloured light brown. 



Fig. 228. Twig of Silver-fir attacked by 

 L. nerviseqiiiuni. + 



a Unaffected needles. 

 b Attacked needles turning brown. 

 c Needles with ripe sporophores. 



