A NEW DISEASE ON THE LARCH IN SCOTLAND. I 99 



^■Ecidium {Peridermium) Laricis^ and, although the form 

 under discussion does not agree in all respects with Klebahn's 

 description, the differences are too slight to justify the creation 

 of a new species. In the same paper Klebahn shows that 

 ^£ddium {Feridermium) Laricis is the fficidial stage of Melamp- 

 sordhim betulinum. 



As the occurrence of Peridermium Laricis has not been 

 previously recorded in Scotland, the following information may 

 prove of value to those interested in forestry. In his observations 

 of the appearance of the fungus, Mr Grant found that the larch 

 was attacked early in the season, and that the fungus was fully 

 developed on leaves when they were about three weeks old. 

 It is interesting to note that, in his subsequent observations, 

 he found the branches had shed their diseased leaves by 30th 

 July, and, in consequence, no further material was available 

 for examination. This would indicate that the stage of the 

 fungus upon the larch runs a rapid course, and may thus 

 account to some extent for the fact that it has previously escaped 

 observation.- 



The fungus is almost always found on the under surface of 

 the leaves but occasionally on the upper side. The aecidia are 

 arranged in rows on one or both sides of the midrib, and are 

 separated by short, irregular intervals (Figs, i, 2, and 3, PL II.). 

 The number of aecidia on each leaf is variable, but is usually 

 6-15. Each group of spores is enclosed by a delicate white 

 protective covering, the pseudoperidium, which, at maturity, has 

 the form of a cylinder, slightly flattened laterally and open at 

 the upper end. The pseudoperidium varies from "5 -7 mm. in 

 height, '5-7 mm. long and ■3-*4 mm. wide. In the earlier 

 stages it is closed, and then the cylindrical part is terminated 

 by a bluntly conical upper portion (Fig. \b). The ripe a^cidio- 

 spores are set free by the irregular rupture of the apex of the 

 pseudoperidium, and, in consequence, after dehiscence has taken 

 place, this is terminated by a ragged or lacerate margin (Fig. la 



1 Arthur and Kern, in Bull. Torr. Bot. Club, vol. xxxiii. 1906, p. 403, 

 definitely placed this species in the genus Peridermium ; the fungus is therefore 

 described as Peridermium Laricis (Kleb. ), Arth. et Kern, by Saccardo in the 

 Syllogt Ftingoncm, vol. xxi. 1912. 



- A re-examination of diseased larch leaves, sent by Mr Murray, forester 

 at Murthly, Perthshire, in June 1911, shows that the fungus present is an 

 early condition of Pcridermii<m Laricis. 



