REPORT OF THE SICIETY 15 



the very hairy Common Mullein (Verbascum thapsus) is attacked by six leaf 

 inhabiting parasitic fimgi, while but three are reported as occuring on the 

 labrous Moth Mullein (Verbascum blattaria.) 



Morphological structures peculiar to varieties influence susceptibility. 

 Varieties of pears with an open channel from calyx to core are those most 

 susceptible to Fusarium putrefaciens, a fruit-rotting organism. Appel attri- 

 butes the immunity to loose smut in wheat and barley to the closed flowers 

 found in the resistant varieties. Fromme, calls attention to the fact that this 

 cannot be the explanation for resistance in the case of wheat, no varieties 

 of which have closed flowers, according to the information available to him (1). 

 It does however, explain the immunity found among varieties of barley to loose 

 smut, as some varieties of barley undoubtedly have flowers which do not open 

 and expose the stigmas to infection. The rare occurrence of Claviceps purpurea 

 on what is said to be due to the brief and irregular openings of the glumes as 

 maturity (2) . It may be of interest to note that the writer's attention was this 

 spring called to a lot of seed wheat (wild goose variety) that contained conside- 

 rable ergot. 



Let us next consider cases of immunity due to incompatability of the 

 invading organism with the tissued of the plant, or in other words the failure 

 of the organism to accomplish the second stage of infection, the establishment 

 of parasitic relationship with the host. The prevention of this s&cond stage of 

 infection is, in some instances due to the anatomical characters of the host 

 tissue, but more often to bio 'chemical properties of the cells. Examples of 

 structural characters influencing resistance have been observed in plums 

 attacked by Sclerotinia cinerea, and potato tubers infected by Pythium debar- 

 yanum. Some varieties of plums become more liable to rot when they begin 

 to ripen. This is due to a softening of the middle lamellae between the cells 

 which allows the fungus to force its way through the tissues more rapidly (3). 

 In making a physiological study of the parasitism of Pythium debaryanum 

 on the potato tuber, Hawkins and Harvey found that the fungus secretes 

 a toxin which kills the cells, and an enzme which breaks down the middle 

 lamellae but does not affect to any extent the secondary thickenings. They 

 observed that White McCorminck, a potatoe very resistant to Pythium debary- 

 anum has a higher crude fibre contents than that of suceptible varieties. This 

 higher fibre content they attribute to more secondary thickenings in the cell 

 walls. Resistance to infection, they found, is apparently due to the resistance 

 of the cell walls to mechanical puncture by the invading hyphae (4). 



When we come to consider cases of immunity due to bio-chemical properties 

 of the cells we find ourselves confronted with many complicated theories, some 



1. Fromme, F.D. Phytopath. II: 507-510. D. 1921. 



2. Stager, R. Mitt, naturforach, Gesellch, Bern. 1922, pp. 11-20, 1923. 



3. Valleau, I.e. 



4. Hawkins, Lona and Harvey, Rodney B. Jor. Agr. Rea. 18, No 5, Dec. 1, 1919. 



