INJURIES INDUCED BY PLANTS 191 



form the trenches at such a distance from the diseased gaps as 

 to warrant the assumption that all trees already infected are 

 included in the isolated area. As a rule it suffices to include the 

 trees nearest to the margin of the gap. If the workman notices 

 that a dead root crosses the trench, then it will be necessary 

 at that point to divert the course of the trench farther into 

 the wood, otherwise the labour will be in vain. Although this 

 operation is a certain preventive when it is properly performed, 

 its careful supervision is so difficult when conducted on a large 

 scale that I am doubtful if a general adoption of the practice is 

 to be recommended in commercial sylviculture. The objection 

 that the sporophores develop in the trenches does not appear 

 tenable, because it is a simple matter to examine the trenches 

 once a year and to remove such sporophores.* When the fungus 

 appears at many points in a wood, even the most careful isolat- 

 ing is of no avail. The gaps should either be filled up with 

 dicotyledonous trees, or if, for any reason, this is deemed im- 

 practicable and conifers must be employed, then the young trees 

 must be carefully watched so that infected plants may be rooted 

 out and the disease be promptly checked. 



TRAMETES PINI l 



This parasite is exceedingly abundant in the pine woods of 

 North Germany.-)- In South Germany, where it is less common, 

 it is 'met with chiefly in spruce woods. It also occurs in the 

 spruce woods of the Harz, the Thuringian Forest, and Schleswig, 

 as well as in the larch and silver fir woods of the Riesengebirge. 



It produces a so-called bark-shake, ring-shake, or heart- 

 shake, which nearly always commences at a branch, and there- 

 fore usually in the crown of a tree. 



The brown woody sporophores, which attain an age of fifty 

 years, vary in shape between an incrustation and a bracket. In 

 the case of pines and larches they occur only on the part of a 

 stem where a branch has fallen off (Fig. 122), while in spruces 



1 R. Hartig, Wichtige Krankheiten der Waldbaume, p. 43. Zersetzungs- 

 erscheinungen des Holzes, p. 32, Tables V. and VII. 



* [If Brefeld's account of the conidial fructification is correct, this may be 

 a more difficult matter than appears. ED.] 



f [Also occurs in this country. ED.] 



