204 THE ROYAL SOCIETY OF CANADA 



From the foregoing description it is apparent that infection is a 

 much more complicated matter than the mere entry of the stoma by 

 the germ tube. Up to this point, the development of the fungus 

 follows the same course on either a resistant or susceptible host. In 

 a susceptible (tolerant) host the fungus may then continue its growth 

 and complete its cycle with the formation of a new uredinium, all 

 without any apparent inconvenience to the host. In this case, 

 apparent damage only results when the points of infection become so 

 numerous that the host begins to feel the drain on its supply of 

 nutriment. On the other hand, a resistant (intolerant) host may 

 admit the fungus through its stomatal openings, as has been shown, 

 but quickly checks its further progress. The most reasonable ex- 

 planation for the failure of the infection in this case appears to be 

 the starvation of the parasite by the local killing of the intolerant host 

 tissue. It is true that the host cells and the parasitic hyphae appear 

 to die so nearly simultaneously as to make it difficult in some cases to 

 decide which perish first. Nevertheless, the author has found in 

 most cases some indication of disintegration in the host cells before 

 a similar break-down could be observed in the hyphae. This is 

 illustrated in Plate VI, 7 and 8. 



"To whatever the resistance may be due in the last analysis it 

 seems to be a peculiar, delicately balanced condition of the host 

 against specific parasites, a balance which is not maintained in the 

 same way towards any two species or varieties" (Freeman and 

 Johnson). 



Summary of Part II 



1. The fungus enters through the stomata of both resistant and 

 susceptible hosts in the same way. 



2. The susceptible host seems to adjust itself readily to the 

 presence of the fungus, and the latter develops luxuriantly to the 

 completion of its uredinial cycle. 



3. The tissues of a resistant host appear to be intolerant of the 

 fungus. The hyphae sent out by the sub-stomatal vesicles soon 

 perish. It is suggested that the failure of the infection may be due 

 to the starvation of the parasite by the local killing of the host cells. 



4. A recent suggestion by Miss Allen that the resistance of 

 Kanred may be due to the narrow stomatal openings of this variety 

 is not supported. 



