THE ENEMIES OF ENGLISH WOODLANDS 293 



the other hand, we agree with Dr. Carruthers that numerous 

 blisters can be found on young bark which does not show 

 the slightest trace of wound or injury. But if by a wound 

 is meant a microscopic puncture, such as an aphis would 

 make, then we require more proof than that now forth- 

 coming that the spores enter only by such minute punctures, 

 and, further, as to the extent to which two- or three-year- 

 old bark is punctured by aphides. The latter practically 

 spend their summer on the needles, and those that hibernate 

 do so chiefly in the axils of the buds. Do the fungus spores 

 enter through these damaged needles ? If so, then stem 

 blisters ought to be most prevalent on two-year-old shoots, 

 whereas this is far from being the case, as every practical 

 forester knows. Secondly, there is no evidence that the 

 hibernating mother aphis does more than rest on the bud 

 or bark, or that she punctures the latter in any way. Every 

 year a certain number of buds die on most larch shoots, 

 and it is generally these buds that form the nucleus of a 

 blister. But when the extraordinary number of aphides is 

 considered, and their universal distribution over every twig 

 on the tree is taken into account, it seems hardly possible 

 that they can be responsible for the death of about 1 or 

 2 per cent, of these buds, and that their presence can have 

 no fatal effect on the remainder. That spores do effect an 

 entrance at places more or less damaged by aphides is quite 

 probable, as on badly infested trees it would hardly be 

 possible for them to enter otherwise ; but the connection 

 between the presence of the aphis and that of the blister 

 does not seem clearly enough proven to justify any satis- 

 factory conclusions on this point to be made. 



As regards the statement that bark is not infected when 

 over four or five years, we think this is not conclusively 

 proved, although it may be true in a general way. On the 

 stems of fast-growing trees there are always cracks and 

 fissures in the true bark which penetrates to the bast below, 

 and there seems no good reason why a spore which has been 

 washed or blown into one of these fissures should not effect 

 an entrance as readily as on young bark. In any case, we 

 have found the fungus growing on bark at least eight or ten 

 years of age, and an examination of the bast below revealed 



