S. p. Wiltshire 281 



against the autumn infection. Trials may sliow that winter spraying 

 immediately after defoliation is effective. 



Summary. 



The infection of apple trees by the canker fungus through scab 

 infections is described. 



The conidia ahghting on the exposed scab stroma give rise to a 

 mycelium which attacks the latter and then grows out into the cortex. 

 The fungus is able to pass through any immature cork layer and finally 

 reach the wood. 



EXPLANATION OF PLATE XM. 



Fig. I. Young stage in the canker infection of a scab wound. Variety, Lord Suffield. 



Jan. 16, 1922. x 1-5. 

 Fig. 2. Similar infections to Fig. 1, but slightly more advanced. Variety, Ecklinville. 



xO-7. 

 Fig. 3. As Fig. 2, but further developed. Variety, Lord Suffield. Jan. 16, 1922. x 1-8. 

 Fig. 4. As Fig. 3. Variety, Lord Suffield. Jan. 16, 1922. Note the original scab from which 



the infection started, x l-S. 

 Fig. 5. A very active infection on a vigorous shoot of Lord Suffield. Jan. 14, 1922. x lo. 

 Fig. 6. Very active canker in late stage of development. Variety, Lord Suffield. Jan. ] 6, 



1922. xId. 

 Fig. 7. Mature canker infection of scab wound. March 3, 1922. x 0-8. 

 Fig. 8. Camera lucida drawing of young canker pustule on outside of a scab infection. 



Variety, King of the Pippins. Nov. 1921. x 420. 

 Fig. 9. A trans, section through a young infection of a scab wound by Nectria galUgena. 



King of the Pippins. Nov. 1921. x 38. 

 Fig. 10. Central portion of Fig. 9 enlarged to show the Nectria mycelium (a, b) growing 



on the Venturia inaequalis mycelium (c, d). Note the characteristic conidia of Nectria 



galligena. x 250. 

 Fig. 11. Trans, section of an infection showing the formation of hyphal strands of Nectria 



galligena. A young strand can be seen at A, and an older one at B, both strands 



being derived from the sub-epidermal mycelia C. 

 Fig. 12. Adjacent section to that of Fig. 11, showing the penetration of the young phellogen 



at D. The other lettering corresponds to that of Fig. 11. 

 Fig. 13. Trans, section through a canker infection of a scab pustule (a) showing the growth 



of the mycelial strand of Nectria (h) through the phellogen [p) into the cortex. A 



new phellogen (p') is organised around the advancing mycelium, x 48. 



REFERENCES. 



WiLTSfflRE, S. P. (1921). Ann. App. Biol vm. 185. 

 (1913). Rrit. Ass. Report. 



{Received April Qth, 1922.) 



