335 



INFECTION AND IMMUNITY STUDIES ON THE 

 APPLE AND PEAR SCAB FUNGI {VENTURIA 

 INAEQUALIS AND V. PIRINA). 



By S. p. WILTSHIRE, B.Sc. 



(With Plates XIX— XXII.) 



The diseases of apple and pear caused by Venturia inaequalis (Cke.) 

 and V. pirina (Aderh.) exhibit many interesting phenomena with regard 

 to the resistance and susceptibility of varieties of the hosts. The 

 investigations described in this paper were commenced with the object 

 of discovering the method by which these fungi attack their hosts, in 

 order finally to investigate the features concerning the question of 

 relative immunity. Notwithstanding the rather considerable amount 

 of work which has been done on these diseases — especially the extensive 

 reports of the Agricultural Stations of the United States — little definite 

 knowledge is available, either as to the minute details of infection or 

 the power of resistance of attacked varieties. The recent paper of 

 Wallace^ contains an exhaustive review of previous work on these 

 diseases : here therefore it is unnecessary to do more than make a brief 

 reference to those points which concern the subjects dealt with in this 

 paper. 



The previous work which has been done with regard to the infection 

 of Venturia is limited to comparatively few papers. Aderhold's work^ 

 on these fungi is by far the most important that has ever been published, 

 and to him we are indebted for most of our knowledge of them. In 

 his description of the germ tube he states that it broadens slightly at 

 the point of entrance, which is usually directly over the junction of 

 two or more epidermal cells, and bores directly through it. He mentions 

 that the appressoria are frequently surrounded by a zone of mucilaginous 

 material, but his figures show no signs of the collar which is described 

 below, neither do they indicate the characteristic sub-cuticular mycelium. 



^ Wallace, Scab Disease of Apples. Cornell Univ. Agric. Exp. Station, Bull. 335. 

 '" Aderliold, R.. Pic Fiisirladien utiserpr Ohstlidntne Land. Jnhrh. XXV, 87.')-!>I4. 



