HEART-ROT 107 



white, and does 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 \ 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 



