184 On Diseases of Plum Trees 



brown ; on these, after a considerable interval, numerous crater-like or 

 lenticular fructifications develop, which almost invariably prove to be 

 pycnidia. A certain amount of gum appears at the junction areas, but 

 considering the proneness of plum trees to gum production its presence 

 cannot be taken as a characteristic of these diseases. 



This general description holds for all the trees examined, but there 

 are differences in detail considerable enough to warrant separate 

 treatment. The following record indicates the nature of these. 



A. Victoria. 



All the specimens, with one exception, were from trees on plantations 

 at Willingham, Cambridgeshire. 



(1) A small shoot from an old tree, of which large lateral branches, 

 six years of age, were affected. The shoot was dead. Numerous 

 small crater-like swellings, 1 mm. in diameter, of the bark were in 

 evidence, due to hard pycnidia, seated in the deeper cortical layers. 

 These pycnidia were seated on a poorly developed, dirty-white stroma, 

 sharply limited from the surrounding tissues by a dark tough "skin." 

 Each pycnidium had a single central pore, and was many-chambered ; 

 the walls were lined with sparingly-branched hyaline conidiophores, so 

 closely packed as to form a palisade-like tissue. 



The spores, borne singly at the tips of conidiophore branches, were 

 continuous, sickle-shaped, hyaline bodies, averaging 7 /u, long, and l"5/x 

 broad, with two oil bodies. In moist weather, they are extruded in 

 enormous numbers as pink tendrils, semi-gelatinous at first, becoming 

 horny on drying. On wetting, the tendrils disintegrate into their com- 

 ponent spores. 



(2) A tree about five years old, from the University Farm, Cam- 

 bridge, was cut down in August, 1913, and kept exposed on the 

 laboratory roof till the following October. It had then developed 

 numerous pycnidia borne several on each erumpent oval dark stroma. 

 As no traces of this fungus were present in August it must here have 

 developed as a saprophyte. Each pycnidium had several pores. Pink 

 tendrils were extruded, made up of spores similar to those described 

 above, but 5 /* long by 1 fx broad. 



(3) A tree nine years old, dead. This specimen was taken 18 ins. 

 from the ground line region, which was also the point of attack. The 

 upper part of the tree was still green. The stromata were black, 

 erumpent, and lenticular; each bearing several pycnidia (Figs. 1 and 2). 

 Over the exterior of each fissure was a thin white covering, specially 



