SPRUCE NECTRIA. 



453 



appear in the bank, which may run into one another like felt. 

 Conidia issue from them from late in the autumn till the 

 spring, and infect surrounding plants through any wounds 

 they may have, and spread the disease. 



The branching mycelium grows chiefly in the sieve-tubes of 

 the soft bast and* the intercellular spaces 

 between them. The growth of the fungus 

 is very rapid, but appears to proceed 

 chiefly in the season of rest of the bark- 

 tissues, not in that of their vegetation, 

 when it is usually arrested. When the 

 fungus has spread all round the stem, 

 the tree dies, or at least that part of it 

 which is above the point of attack. If 

 however, the diseased tree can retain any 

 sound bark on one side till the ensuing 

 spring, it is saved, for it protects itself 

 by producing a corky sheath between the 

 sound and diseased part, which stops 

 the further progress of the fungus. 

 The dead bark is then thrown off, and 

 the cankerous place grown over. 



' 1). Subjects of Attack, and Distribution. 



The fungus appears chiefly on young 

 spruce from three to thirteen feet in 

 height, and both in pure spruce woods 

 and in mixtures of spruce and beech. 

 It has also been observed on Cembran 

 pine and larch. It is very common 

 in frosty localities. The conidia gain 

 admission to the tissues only through 

 external wounds, which are therefore 



extremely dangerous in localities where a Clusters of gporocarps 

 the fungus is present. Badly-growing O n the dead bark, 

 plants are the more subject to its attacks, 



as injuries by insect or hail heal up less readily than in 

 the case of vigorous plants, and are therefore longer exposed 

 to the attacks of the fungus. 



Fig. 221. Spruce 

 attacked by Nectria 

 " la, Fr. 



