APPLE-TREE CANKER 129 



particular point, and then moving to another, resulting in 

 the canker spots having a very irregular outline. 



At those points of the wound where the mycelium is 

 most vigorous, small white cushions or stromata appear in 

 the autumn, bearing on their surface very minute conidia, 

 which become free at maturity, and germinate at once. 



During the following spring, a second form of fruit, con- 

 sisting of clusters of minute, blood-red perithecia, appear 

 on the cushions which during the previous autumn bore 

 conidia. These perithecia contain in their interior numer- 

 ous asci, each enclosing eight spores. 



Preventive Means. — Badly diseased branches should 

 be removed and burned. Where the canker is slight the 

 affected part should be cut out, and the wound coated 

 with tar. 



Hartig has observed that aphides are often present along 

 with the fungus, and these may assist in spreading the 

 disease by carrying conidia, and even unconsciously intro- 

 duce them into the punctures they make, hence it would 

 be advisable to apply an insecticide. 



Old cankered fruit-trees that have been destroyed by 

 this or other fungi are too frequently allowed to remain 

 standing long after it is admitted that they are of no value, 

 except for firewood. Such trees are in reality acting as 

 nurseries for the growth and dispersion of fungus parasites, 

 and should be removed without delay. 



Plowright, Gard. Chron., April 19, 1884, figs. 

 Hartig and Somerville, Diseases of Trees (Engl, ed.), 

 p. 91. 



