H. WORMALD 31 



ir. THE FUNGUS. 



(a) Annual Cycle. 



Although the newly killed twigs did not as a rule bear any fungous 

 fructifications except in those comparatively rare instances where 

 Monilia pustules appeared on the leaves, the presence of M. cinerea on 

 the dead twigs of the previous season suggested that the fungus would 

 appear at the surface of the young affected twigs if these were allowed 

 to remain on the trees until the following year. This seemed all the more 

 probable by analogy with the annual cycle of that form of Monilia 

 cinerea which produces the "Blossom Wilt and Canker" disease of apple 

 trees. In a previous paper it has been shown that in the latter the 

 pustules are not generally produced at the surface of the cankers and the 

 dead spurs until the approach of winter, but develop readily from about 

 the beginning of December onward through the winter and spring. 



In order to ascertain whether similar conditions obtained in the case 

 of the " AVither Tip" fungus, labels were attached to a number of the dead 

 twigs in the summer of 1916. As was anticipated, grey Monilia pustules 

 began to burst through the bark of some of the twigs early in December 

 (a few being found with immature pustules on December 6) and con- 

 tinued to appear throughout the winter. With very few exceptions all 

 the twigs labelled as showing the typical wither tip condition in the 

 summer, bore Monilia pustules in winter. Thus on one tree 31 withered 

 tips had been labelled in August 1916. Monilia pustules were first 

 observed on December 6 when one of the dead twigs was found bearing 

 the fungus, as pustular tufts of conidiophores, on its surface; later, 

 pustules appeared on others and by May 1917 they were present on all 

 except two of the labelled twigs. 



The length of the dead portion had been noted in the case of some of 

 them and in no instance could evidence be found that the fungus had 

 extended any further along the twigs from August 2, 1916, to May 11, 

 1917. In this again the habit of the fungus found on the plum twigs is 

 comparable with that of the form found on apple spurs and cankers for 

 it has been shown that although the blossom- wilt fungus of apple trees 

 makes rapid progress for a few weeks immediately after infection of the 

 flower occurs its further extension into the tree is inhibited after about 

 the middle of July, 



On another tree 25 withered tips had been labelled on August 5, 1916; 

 the Monilia appeared at the surface of three of them by December 6 and 

 all bore mature pustules on May 14, 1917, when the tree was in full 



