S. p. Wiltshire 183 



conditions are not pruned) some of the varieties canker very badly and 

 in these cases leaf scar infection is almost wholly responsible. 



The association of canker with buds has been pointed out by Goethe (3), 



Excellent material for studying this method of infection was afforded 

 by some trees raised in the course of fruit-breeding work at Long Ashton. 

 They were seedhngs of the cross Kingston Black x Medaille d'Or, two cider 

 varieties, and developed canker very freely. In August 1919 numerous 

 examples of young cankers evidently started from buds formed in the 

 preceding autumn were found and these left no doubt that the canker 

 fungus could enter the tree by some means in the region of the buds. 

 Continuous observations have since been made on these trees. 



The first point noticed was that the cankers on the 1918 wood were 

 considerably in excess of those formed in the previous years. Counts of 

 the cankers on the wood formed in five consecutive years gave the follow- 

 ing results: on the 1915 wood, 1 canker; on the 1916, 4; on the 1917, 29; 

 and on the 1918, 434. The number of 1919 was over 600, but exact figures 

 were not obtained. On these trees, infection of the shoots took place 

 during the year succeeding their formation, viz. the 1915 wood was 

 infected in 1916, the 1916 in 1917 and so on. The trees in question had 

 never been pruned and therefore the number of cankers formed on the 

 growth of any one year gave an indication of the number of infections 

 occurring during the following season. 



The number of infections in some cases was exceedingly high. Taking 

 a single branch of one of the trees, not more than 1 A ins. in diameter at 

 its base and about four to five years old, almost every bud of the 1918 

 wood on that branch was cankered, the numbers reaching the very large 

 total of 65. Besides the actual cankers, there were cases where the buds 

 of 1918 failed to develop in the spring of 1919 and were possibly killed 

 off by the fungus or at least so injured as to be unable to develop whilst 

 the main stem remained uninfected. Such shoots, during August, showed 

 long stretches of bare stem, and a tree severely attacked presented a 

 partially defoUated appearance. 



Large numbers of bud infections having been observed on the trees 

 above mentioned, search w^as made to find similar infections on other 

 varieties. Leaf scar infection was found to be extremely common, in 

 fact so widespread as to give the impression that it would affect any 

 variety provided the conditions were favourable. It has been found on 

 Warner's King, Bramley"s Seedling, James Grieve, King of the Pippins, 

 Lord SuflEield, Devonshire Quarrenden, AVhite Transparent, Royal 

 Jubilee and many other dessert and cuUnary varieties and also on many 



Ann. Biol, vm 13 



