CHAP, xiii.] Fungoid Diseases of Trees 293 



are not safe against attack until about thirty years old. It 

 occurs principally on wet soils, and after cold damp springs. 



The mycelium of this fungus develops itself in the green 

 parenchym of the bark of the youngest shoots, within which 

 it is perennial, and extends itself into the new shoots when they 

 flush in May. Shoots thus taken possession of by the mycelial 

 filaments show a brownish discolouration of the woody tissue 

 right into the pith. Before the shoots have attained their full 

 length, pale yellow spots, bearing within the bark-parenchym 

 the spermogonia of the fungus, become apparent about the 

 end of May or the beginning of June, from the middle towards 

 the end of the shoots. With the development of the sporidia 

 under the bark the light yellow spots turn reddish-yellow, and 

 become raised like pustules until the epidermis at last fissures 

 longitudinally, and the spores are scattered. Each such fissure 

 produces slight hypertrophy ; and, as the cellular tissue dies 

 down as far as the woody substance, this necessitates a bend 

 in the shoot, which becomes concave at the diseased part, and 

 at the same time naturally shows an outflow of resin. If the 

 damage is only slight the wound cicatrizes and in time becomes 

 obliterated ; but when eruptions of spermogonia take place, as 

 often happens, on alternate sides, a peculiar twisted form of 

 growth is characteristic of this disease. When damp weather 

 in May and June favours the development of the fungus during 

 successive years, the shoots of the young Pines often become 

 completely deformed ; portions of them die off wherever the 

 disease extends all round the shoot so as to stop the circula- 

 tion of sap, and the young plants assume a somewhat frost- 

 bitten appearance. The side-shoots which endeavour to 

 assume the place of the leading shoots also usually become 

 infected. 



This fungus has an undoubted change of generation with 

 Melampsora tremulae occurring on Aspen, whose teleutospores, 

 produced in the following spring, develop the original form 

 Caeoma pinitorquum. 



