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 hi 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 n, 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 ft 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 



