HEART-ROT 107 
white, and docs not grow out much from the substratum, 
and appears finely granular. Conidiophores are produced 
in six to ten days, and may constantly be found afterwards. 
Cultures obtained from basidiospores or conidia differ in 
no way from those grown from diseased wood, but the risk 
of including impurities is reduced. Cultures will also grow 
on moistened sterilized bread, but they are not very vigorous 
on this medium. , 
Cultures on natural media. Cultures were grown on 
1. Sterilized larch twigs with bark. 
2. Sterilized blocks of larch wood, composed of heart- 
wood or sap-wood or both. 
3. Sterilized roots of (a) larch, (b) Weymouth pine. 
4, Soils from various localities. 
Unless otherwise stated, inoculations were made by 
placing small pieces of gelatine or agar-agar containing 
‘mycelium on the substratum which was to be infected. 
1. Larch twigs 2-3 in. long and 4} in. in diameter were 
placed on damp cotton-wool in Erlenmeyer flasks and test- 
tubes. On sterilizing in the autoclave the cotton-wool 
became slightly stained by liquid running down from the 
twigs. Mycelium placed on these twigs grew fairly rapidly, 
and at room temperature completely covered them in about 
six weeks, and even spread on to the cotton-wool at the 
bottom of the flasks. A much more woolly mycelium was 
produced on larch twigs than in gelatine or agar-agar 
cultures, and conidiophores were everywhere abundant. 
Mycelium penetrated the periderm, cortex, phloem, and 
wood. 
2. Cultures on larch blocks were very similar. The 
mycelium grew much more rapidly on the surface of the 
blocks than inside, especially when the air was thoroughly 
damp. When the cotton-wool at the base of the test-tube 
was only slightly moistened, the external growth was scarcely 
noticeable, though on addition of more water it became 
quite normal. It is much greater on blocks of alburnum 
than on duramen. 
The formation of soluble and insoluble gum and the 
