172 A B/(>ss(nit Wilt ({!)(} (Uuilcr of Apple Trees 



the spring of that year began to produce Monilia pustules which burst 

 through the dead bark. In the following month these became somewhat 

 pulverulent and particles of pustules placed in water set free mature 

 conidia. On January 24, 1917, conidia were obtained in this way in 

 a drop of water on a glass slide when the temperature of the air, as 

 registered by a thermometer placed on one of the trees, was 28-5° F. 

 (^ — 2° C). The slide was placed in a damp chamber at a temperature 

 of 6° to 8° C. ; within 24 hours about 50 % of the free conidia had 

 germinated with germ tubes to 52 /x in length. 



This blossom-wilt fungus apparently occurs comparatively rarely on 

 the apples themselves, even on trees severely infected with blossom wilt. 

 On the apple trees at Wye it has been observed on the fruit on one 

 occasion only when it was found on a few very young apples soon after 

 they had set. In a plantation of Lord Derby trees in the Weald of 

 Kent there were found in January 1916 small "mummified" apples 

 nearly covered with a Monilia which in cultures was indistinguishable 

 from that found on the cankers ; in the same plantation in mid-July 

 1915 (and again in 1916) a few young apples, about 1-5 cm. in length, 

 were obtained, apparently killed by the same fungus which appeared in 

 the form of numerous pustules bursting through the skin. I have not 

 yet seen this form on fully grown naturally infected apples. 



(c) CoiHjjarifson, tvitlt other diseases produciny a sliiiilar condition. 



It is sometimes impossible to distinguish, from their general appear- 

 ance, between the Monilia cankers and those produced by Nedria 

 ditissima ; the latter are usually recognised by the increased rate of 

 growth (set up in the tissues bordering the canker) which causes the 

 branch at that place to be swollen. Young Nectria cankers, also, 

 generally bear the sporodochia of the Fusarium stage in the summer, 

 or the pustules if not evident readily develop when placed in a damp 

 chamber ; young Monilia cankers do not produce pustules until about 

 December. Again Nectria cankers originate at nodes bearing unopened 

 buds, or infection occurs through wounds ; those produced by the 

 blossom-wilt fungus arise around the insertion of infected flowering 

 spurs. 



The blossom-wilt condition bears a close resemblance to that caused 

 by the Apple Sucker {Psylla mali) ; when the damage is caused by this 

 insect, however, numerous cast skins are to be found attached to the 

 under side of the withered leaves. The larva of the Pith Moth also 

 produces a withering of the fruit buds but before the flowers themselves 



