New DIsEASE ON LARCH IN SCOTLAND. 81 
Lancis produces orange-yellow spots on the leaves, but is 
at once distinguished from Peridermium Laricis by the entire 
absence of the pseudoperidium, as well as by differences in the 
sculpturing of the spore wall. Caeoma Laricis has been shown 
by Klebahn and others to be the aecidial stage of six different 
species of Melampsora, in which the uredospore and teleutospore 
stages occur on various species of Populus and Salix 
Although no definite record of the occurrence of Peridermium 
Laricts in Great Britain or Ireland has been made it is probable 
that Plowright,* in 1891, carried out experiments with this species. 
This investigator discovered a form of Cacoma Laricis near King’s 
Lynn, the aecidiospores of which, when placed on Betula alba, 
caused infection, and, in course of time, the uredospore and 
teleutospore stages of Melampsora betulina were produced. A 
subsequent infection of Larix europaea by the germinating 
teleutospores produced spermogonia only. 
Klebahn,t by infection experiments commenced in 1896 in the 
neighbourhood of Hamburg, conclusively proved that Perider- 
mium Laricts is the aecidial condition of Melampsora betulina. 
In his earlier experiments spermogonia were formed on Larix 
europaea as the result of infection by teleutospores from the birch, 
but, in later investigations, aecidia only were produced. 
Melampsora betulina differs from the remaining species of the 
genus in the presence of a pseudoperidium enclosing the ure- 
dospore sorus. Klebahn + has therefore instituted a new genus 
Melampsoridium for the reception of this species. The differ- 
ences between the two genera are as follows :— 
Melampsoridium: Aecidium of the Peridermium type. 
Uredospore sorus with a definite pseudoperidium. 
Melampsora: Aecidium of the Caeoma type. Uredospore 
sorus surrounded by capitate hairs but without a definite 
pseudoperidium. 
The teleutospore sorus is similar in each genus. 
Arthur and Kern ¢ include Peridermium Laricis in their list 
of North American species since Melampsoridium betulinum is of 
common occurrence in that country ; the stage on the larch has 
not yet, however, been found in North America. Saccardo § 
records its occurrence in France and Germany. 
The specimens of Peridermium Laricis obtained in Scotland 
differ in some respects from those described by Klebahn. Up to 
the — no spermogonia have been discovered ; it is possible, 
i Impfversuche mit Rostpilzen. Zeitschr. f. Pflanzenkr., Bd. i, 
on as cit. and ee ei mit Rostpilzen. Bericht viii(1899). Jahrb. 
‘, alee be Bd, xxxiv, 1900, p. 347. 
$L 
§ slog ‘Fungorum, vol, xxi, ‘ 
