264 TIMBER AND SOME OF ITS DISEASES. [CHAP. 



measures seem to be, to cut down the diseased trees 

 of course this should be done in the winter, or at 

 least before the spores come and use the timber as 

 best may be ; but we must first see whether such a 

 suggestion needs modifying, after learning more 

 about the fungus and its habits. It appears clear, 

 at any rate, however, that every diseased tree removed 

 means a source of aecidiospores the less. 



FIG. 40. Section across an old pine-stem in the cancerous region injured by Perider- 

 fniutn Pini (var. corticola). As shown by the figures, the stem was fifteen years 

 old when the ravages of the fungus began to affect the cambium near a. The 

 mycelium, spreading in the cortex and cambium on all sides, gradually restricted 

 the action of the latter more and more : at thirty years old, the still sound 

 cambium only extended half-way round the stem no wood being developed on 

 the opposite side. By the time the tree was eighty years old, only the small area 

 of cambium indicated by the thin line marked 80 was still alive ; and soon after- 

 wards the stem was completely "ringed," and dead, all the tissues being suffused 

 with resin. (After Hartig.) 



Probably every one knows the common groundsel 

 (Senecio vulgaris) which abounds all over Britain and 

 the Continent, and no doubt many of my readers are 

 acquainted with other species of the same genus to 

 which the groundsel belongs, and especially with the 

 ragwort (Senecio Jacobcea). It has long been known 





