LEAF AND SEEDLING DISEASES 169 
noted in 1883, and was then attributed to damp atmosphere 
inhibiting transpiration. Subsequently the disease became 
much more frequent, and in some woods, especially in 
Upper Bavaria, the greater part of the needles have been 
known to fall by the beginning of August, and in September 
many trees have become entirely defoliated. The disease 
is much less destructive at altitudes above 3,000 ft. 
The first evidence of the disease is the appearance of 
small or large brown patches on the leaves in July. The 
leaves remain on the trees for a time, and on the brown 
patches there appear small black conidia-bearing pustules. 
The pustules are very small, only 0-1 to 0-3 mm. across, but 
arise in groups. The leaves begin to fall in the latter part 
of July, especially from the lower part of the crown where 
the air is moister. 
Diseased needles contain much colourless mycelium, both 
in and between the cells. The protoplasm of the cells 
contracts away from the walls, but in the inner part of the 
leaf the green colour remains and is actually persistent till 
winter or the following spring, though it is masked by the 
brown pigment in the outer parts of the needle. The 
mycelium gives rise to the conidial pustules which are 
formed below the epidermis and break through it in circles. 
The conidia are of two sorts, each borne on the ends of very 
fine hyphae. First there are very small conidia, 3 x 1 », which 
do not germinate in culture solutions. These have been 
described under the name of. Leptostroma laricinum and also 
as spermogonia of Lophodermium laricinum. Next there are 
elongated needle-shaped conidia, 30» long, which are borne 
on larger basidia near the outside of the pustules. They 
are at first non-septate, but later divide up into four seg- 
ments. They break off easily, and are distributed either 
by wind or by being washed off by rain, when they fall on 
to the lower branches and leaves. The latter are readily 
infected, as germination takes place in a few hours, and 
new pustules appear on these leaves in about three weeks. 
Thus when once the fungus has appeared there is always 
a tendency for it to infect the lower branches rather than 
the upper. Also wet years and wet places are especially 
