144 



DISEASES OF TREES 



organized by the fungus which causes the disease as we shall 

 see presently that the shoot bends sharply over at that point 

 under its own weight, as though it had been fractured at the 

 base. Very frequently death spreads back from the base of the 

 youngest shoot to the apex of the shoot of the previous year 

 (Fig. 8 1, <:), in which case the young lateral shoots that are 

 situated there also succumb (Fig. 82, a). 



As already indicated, this may, in May or early in June, be 



mistaken for damage due 

 to frost, although the latter 

 is generally confined to cer- 

 tain localities, appears sud- 

 denly on a great number 

 of shoots, and is character- 

 ised by all the affected 

 leaves dying simultaneous- 

 ly. The disease at present 

 under discussion has no re- 

 lation whatever to frost. 

 Shoots that have succumb- 

 ed to this disease also bear 

 a certain resemblance in 

 many cases to those dam- 

 aged by Chermes abietis ; 

 the galls which the latter 

 induces at the base of the 

 shoots being often so small 

 as not to be visible on the 

 upper side, and in both 

 cases there is a deflexion of 

 the shoot downwards. 



In the course of the summer the dead shoots display spore- 

 receptacles (pycnidia) in greater or less abundance in the form 

 of very minute black tubercles. These are so small as just to be 

 visible to the naked eye, and are very often to be found only 

 amongst the bud-scales at the base of the dead shoot. In other 

 cases they are also to be met with higher up ; in fact, they are 

 often specially abundant on the shrunken shoot-apex (Fig. 82, a)- 

 They either rupture the epidermis of the shoot or occur on the 



FIG. 81. a, a young diseased spruce branch, 

 the apex of which is still green and fresh. 

 b, a leaf attacked by disease towards the 

 base, twice natural size, c, apex of a 

 two-year-old shoot, into which the disease 

 has spread backwards from the younger 

 shoot. The brown discoloration of- the 

 cortex and pith is indicated by shading. 



