170 A Bhssom Wilt find Ctnthrr af AppJr Trees 



From May 17 to tlic end of that month other trusses wilted and the 

 following sequence was recorded for one tree: 



Date Affected trusses 



May 17 2 trusses wilting (leaves beginning to Hag) 



„ 22 5 trusses dead : 2 others wilting 



„ 27 18 trusses dead: 1 wilting 



„ 31 19 trusses dead. 



No trusses on this tree began to wilt after May 31. 

 In all cases where wilting of trusses occurred subsequently to May 31 

 they were found to be killed not by a direct infection through the blossom 

 but bv the development of the disease in the spur or branch from 

 infection through flowers of other trusses. In several instances a spur 

 bore two trusses one of which became infected directly and the fungus 

 penetrated the tissues of the spur to the level of insertion of the un- 

 infected truss which, in consequence of the interruption to the upward 

 flow of sap to it, wilted from desiccation. 



As an illustration of the rapid progress made by the fungus during 

 the month of May the condition of a small branch which was completely 

 girdled by the 31st of that month may be cited ; on that day the shoots 

 and trusses borne at the nine nodes commencing at the distal extremity 

 were as follows : 



Node 1. Vegetative shoot wilting (leaves yellow and drooping). 

 ,, 2. Barren spur wilting. 

 ,, 3. Dead truss with canker girdling the branch and extending 



1 cm. upwards and 2-5 cm. downwards. 

 ,, 4. Dead truss with canker nearly girdling branch. 

 ,, 5. ,, ,, ,, halfway round. 



,, 6. ., ,, ,, nearly half round. 



,, 7. Living healthy truss of flowers. 

 ,, 8. Dead truss with canker just beginning. 

 ,, 9. Living truss. 

 The trusses at nodes 3, 4, 5, 6 and 8 had been killed by direct infection 

 while the shoots at nodes 1 and 2 were wilting by reason of the girdling 

 canker at node 3; all the spurs were unbranched and about 1*5 cm. in 

 length; the branch, where girdled, was 0-8 cm. in diameter. 



As infection probably did not occur before May 1 it will be seen 

 that in the course of about four weeks conidia had germinated and 

 produced mycelium which had traversed the tissues of the flowers and 

 the spurs and had invaded the branch itself to a distance of two and a 

 half centimetres. 



