82 BorTHWICK AND WILSON 
however, that these develop earlier than the aecidia, and have, 
in consequence, been overlooked. The colour of the pseudo- 
peridium is described by Klebahn as bright red-orange (‘“ hell 
rotlich-orange’’). In the Scottish specimens, in the early stages 
before the pseudoperidium had opened, the colour was pale 
yellow, and, after dehiscence, it became white 
Considering the abundance of Melampsoridium betulinum in 
this country, it is a remarkable fact that Peridermium Laricts is 
of such rare occurrence. Its resemblance to Caeoma Laricis may, 
however, partly explain the absence of previous records, It is 
possible that Melampsoridium betulinum really consists of several 
physiological species, and that Peridermium Laricts is only one of 
its aecidial forms; this supposition may explain the absence of 
records from North America. At present no information is avail- 
able on this point, but it is proposed to carry out infection experi- 
ments to throw light on this and other questions in connection 
with the life history of the fungus. 
DESCRIPTION OF PLATE XIII. 
All figures refer to Peridermium Laricis. 
Fig. 1.—Photograph of twig of Larix europaea showing diseased leaves: (a) 
doperidium showing lacerate margin (short pointer) ; ()) un- 
d pseudo-peridium (long pointer) (x 4). 
Fig. 2. Putra of twig of Larix europaea showing diseased leaves : (a) fused 
pseudoperidia (x 
Fic. 3.—Photograph of twigs of Lae europaea showing diseased leaves (about 
natural size). 
Fic. 4.—A pseudoperidium showing lacerate margin (x about 50). 
Fig. 5.—Spore in surface view (x 
Fic. 6.—Spore in optical median section (x 1000). 
Fic. 7.—Part of pseudoperidium ; the lower cells show the verrucose marking 
n the walls (x 220 
