NECTRIA 185 



wards the wood is also destroyed, the canker often completely 

 girdling small branches, which are then easily broken off by 

 wind. As a rule a rugged callus forms round the wound, 

 and frequently new canker spots appear on a branch at 

 points where there is no evidence of external inoculation, 

 and Hartig considers that the mycelium travels under the 

 bark for some distance from a point of infection. At those 

 points where the mycelium is most vigorous, minute, small, 

 white cushions or stromata appear in the autumn, bearing on 

 their surface minute conidia. During the following spring 

 clusters of small, bright-red perithecia appear on the edges 

 of the wound. 



Perithecia usually in dense clusters, globose, papillate, 

 blood-red, asci cylindric, 8-spored, spores ovate-oblong, i-sep- 

 tate, hyaline, 14X5-6 /*. 



Conidial form (Tubercularia crassostipitata, Fckl.). Conidia 

 ovate-oblong, continuous, 6-8 x 3-4 /*. 



Badly diseased branches should be removed and burned. 

 Where the canker is slight, or when it is located on the 

 larger branches, the diseased portions should be cut out, and 

 the wounds at once dressed with gas-tar. Old, cankered trees 

 are too frequently allowed to remain standing after they are 

 useless. All such should be removed and burned. 



The American woolly aphis and green fly should be kept 

 down by the use of insecticides. 



Hartig and Somerville, Diseases of Trees, p. 9 1 . 



Spruce Nectria (Nectria cucurbitula, Fr.) has been shown 

 by Hartig to be a destructive wound-parasite, attacking more 

 especially the spruce, less frequently the silver fir and Scots 

 fir. The bark is the part attacked, an entrance being effected 

 through wounds made by the larva of the moth called 

 Grapholitha pactolina, also through bruises caused by hail- 

 stones or broken branches. Both conidia and ascophores are 

 capable of infecting the tree ; the spores germinate on the 

 resin surrounding a wound, and the mycelium penetrates to 

 the cambium zone, where it is enabled to live and spread 

 throughout the year. From thence it extends to the wood 

 and flourishes most luxuriantly in the sieve-tubes and soft 

 bast, growing most actively during the winter months when 

 the growth of the tree is at a standstill. Some time after 

 infection the bark is killed and dries up during the summer, 



