133 



CANKER IN APPLE TEEES. 



Theke are probably several diseased conditions of Apple trees known as canker. 

 During the past two or three months I have been looking into this disease some- 

 what attentively, and I have come to the conclusion that the commonest and most 

 serious form is due, as was pointed out by Goethe, to a sph^riaceous fungus, 

 Nectria dUissima (Tul.)* The various members of Sphwviacei occur, as a rule, 

 upon dead wood-not upon the living tissues of plants. There are, however, 

 many important excepti.ms-such, for example, as the Valsa parmula..a de- 

 scribed many years ago by Mr. Berkeley, upon living Oak tw>gs. More important, 

 from an economic point of view, is the Sph^ria ,uorbosa of Schwein.tz the cause 

 of black knot in Cherry and Plum trees in the United States : closely allied to 

 which is Gibbera vaccinii upon living branches of Vacciniam ntis-Idaa in our own 

 country. The Dothideacece, too, occur, many of them, upon living leaves and 

 branches, as the genus Phyllachora for example. Although there is nothing 

 impossible in the notion that a mctria may be parasitic upon living branches yet 

 I must confess my first impression was, that the fungus found a suitable home 

 upon Apple twigs which were already dead rather than that it was the cause of 

 the death of the affected branches. It is well known that winter and spring are 

 the seasons in which the Sphceriacei as a rule are found in the best condition of 

 fructification. I have, therefore, closely examined cankered Apple trees during 

 the past two months wherever I have had an opportunity of doing so, and in no 

 sin-le instance have I failed to find the Nectria upon every tree examined. It 

 is not implied that every cankered patch was found producing perithccia ; at the 

 same time the majority of the cankers upon each tree were found bearing he 

 fungus in abundance : and, further, it was not found upon any other part of the 

 trees The trees were not confined to one garden nor to one locahty. The 

 specimens which I submitted to the Scientific Committee recently were gathered 

 from (1) Mr. J. Bird's nursery at Downham ; (2) Mr. S. N. Marshall s garden at 

 West Lynn ; (3) Mr. J. T. Stevenson's garden at Clenchwarton ; (4) Mr. C. reelc s 

 orchard at Tilney St. Lawrence ; (5) Mr. G. B. ffolke's garden at Wolferton ; and 

 (6) Mr T. Pung's garden at King's Lynn. When the parasite gains an entry into 

 the bark of a medium-sized branch, which it often doe. through ^ l^t^^^l ^^'^ 

 having been broken or cut (fig 1), it at first causes the death of the bark and 

 subjacent wood to only a limited extent. The bark cracks concentrically ; in the 

 cracks and upon their edges the perithccia are most commonly found. It is 

 obvious that a certain time must elapse between the period of infection and the 

 time at which the mycelium or spawn can develope its perfect fruit. This 

 probably takes some months, for it will be seen by inspecting the specimens them- 



* Nearia Hittissuua. Tul Carp., ul, P, 73, t. . ,, f- 1 "4/=, ^ -canea of many a^^^^^^^^^^^ 

 Perithecia widely scattered or densely gre.ar.ou^goW^^^ P P^^_. „, ^yaline.- 



^.'^l.Si' ="r:W/:'.L^ ?nl"'.,>X. Fuckel, Sy.V. Mycol., p. .So- ovate-oblong, con- 

 tinuous, 6—8 X 3—4 mk. 



