REPORT OF THE SOCIETY 11 



duction of the robust, the acreage of the pea bean is now as large as formerly 

 (1). 



Other promising results with disease resistant plants are those of Coons 

 of Michigan, from his work on seed production of Golden Self-blanching 

 celery resistant to Yellows, (Fusarium sp.) (2) and those obtained b}^ Jagger, 

 who selected eight varieties of lettuce apparently immune to mildew (Bremia 

 lactucae Reg.) in both California and Florida. These varieties were however, 

 all of European origin and not suited to American conditions, so they were 

 hybridized with the popular variety Los Angeles Market or New York, which is 

 sold under the name of Iceberg lettuce. This variety is very susceptible to 

 mildew. The results in the second generation indicate that immunity is in- 

 herited as a simple Mendelian dominant character, so that it is expected that 

 hybridization and selection will give immune strains of New York and other 

 popular varieties of lettuce. 



Let us next consider the nature of immunity and resistance and review 

 the scientific evidence available concerning the causal factors. In any dis- 

 cussion of this kind, one must keep in mind that there is immunity, resistance, 

 apparent resistance or apparent immunity and tolerance, and there is a danger 

 of confusion them. 



True immunity or complete resistance to disease is rare among plants, 

 but we have such examples of it in the varieties of potatoes immune to potata 

 wart or canker; buri cotton in India immune to wilt, caused by Fusarium. 



Resistance, as the term is used by plant pathologists, is in reality relative 

 immunity or relative resistance to infection. Plants which are said to be 

 resistant to a particular parasite are affected by it but the attack is slight as 

 compared with that on the less resistant kinds. Resistance is much more 

 common than immunity. It is recorded as occurring among the various varie- 

 ties of nearly all our cultivated plants. True immunity and resistance being 

 relative terms no attempt will be made to deal with them as separate pheno- 

 mena in this paper. 



Apparent immunity or resistance, which is in reality escape from disease 

 is quite distinct from, and should not be confused with, true immunity or 

 true resistance. Plants may escape disease for various reasons, such as climate 

 and seasonal conditions unsuitable to the parasite; absence or scarcity of 

 insect carriers of the inoculum; absence from the locality of the particular 

 biologic strain of the pathogene capable of infecting the variety supposed to 

 be resistant. In Ontario many of our early potatoes escape late blight and 



1. Burkeholder, W. H. Phvtopothology 14, 1-8, ja. 1924. 



2. Coons, G. H. Miltose, Rav. Phytopathology, 13, 24 Ja. 1923 (Abstract). 



3. Jagger Ivan E. Phytopathology 14, 122, F. 1914 (JAbstract). 



