178 LEAF AND SEEDLING DISEASES 
or aecidial stage. The following account is chiefly taken 
from the work of Klebahn, who has made a very special 
study of the genus Melampsora, and in nearly every case 
he has been the first to determine the identity of the coeoma 
with specifically distinct uredo-forms. The identification of 
the different species is often difficult, even in the uredo- 
stage, and a large number of biological races have arisen. 
Thus species which have their uredo-stage on Salix Caprea 
may have their aecidial stage on larch or spindle-tree, and 
those with uredo-stage on aspen may have their aecidial 
stage on larch, Scots pine, or dog’s mercury. For the 
features by which these species may be distinguished, the 
reader is referred to Klebahn (1904) or Grove (1913), and 
only points of biological interest are mentioned here. 
Melampsora Larici-Caprearum, Kleb. Uredo- and teleuto- 
sori on Salix Caprea, less frequently on Salix aurita and 
other species. 
Melampsora Larici-epitea, Kleb. Uredo- and teleuto-sori 
on many species of Salix. There appear to be many bio- 
logical races of this species, all with their coeomata on the 
larch, but with uredo-stage on different willows. These 
races are indistinguishable morphologically, and it is only 
by infecting the larch with the rust obtained from a par- 
ticular species of willow and then reinfecting various species 
of willow that their validity can be determined. For instance, 
it is found that the rust of this species taken from Salix 
Caprea will, after its generation on the larch, infect S. 
fragilis or S. viminalis, but not S..purpurea, while the race 
which grows on S. purpurea will not infect the other species. 
Melampsora Larici-populina, Kleb. Uredo- and teleuto- 
sori on Populus balsamifera, P. canadensis, P. nigra, and 
P. pyramidalis (italica). The association of this species 
with the coeoma on the larch was first demonstrated by 
Hartig in 1889. 
Melampsora Larici-tremulae, Kleb. Uredo- and teleuto- 
sori on Populus alba, P. tremula, and rarely P. balsamifera. 
The aecidial stage of all these species grows on the larch, 
and produces what is described as Coeoma laricis. On the 
