SEED IMPROVEMENT MEETING. 213 



may not always be due to a difference in soil or climatic condi- 

 tions and its consequent effect upon the host plant but is , as 

 likely to be due to the presence there of another strain of the 

 fungus. It may be that some plants now heralded as immune 

 to certain diseases would become susceptible if attacked by a 

 strain of the fungus from another source. 



The writer has not found any varieties of the kidney bean, 

 Phaseolus vulgaris, that have been resistant to every strain of 

 the bean anthracnose fungus tested. Some varieties are less 

 susceptible than others and it may be that certain varieties not 

 yet tested by the writer may prove entirely immune. The 

 writer does not wish to intimate that he believes no varieties of 

 beans are immune to anthracnose or that the numerous exam- 

 ples of disease-resistant plants that have been obtained by care- 

 ful and painstaking selection and hybridization, are liable to 

 infection from those very diseases they are supposed to be 

 proof against. We do need, however, to use every safeguard 

 against error in this most important work. 



It would seem improper to close without a word regarding 

 the cause of immunity in plants. Not that we have anything 

 definite to contribute, but because speculation regarding it is 

 interesting. Several investigators though their work have done 

 much to clear away confusing ideas and to present something 

 logical. It was once thought that the stucture of the immune 

 plants differed in some way from that of the susceptible ones, 

 so that penetration by the parasite was impossible. The opinion 

 of Marshall Ward, Sahnon, and many plant pathologists is 

 that the structure of the plant in most cases has very little to 

 do with immunity. Ward (13) showed that immimity in the case 

 of those plants affected by the Brome Rusts was due to the 

 very vigor of the parasite itself, which attacked and killed the 

 host cells. As it is unable to live upon dead tissue it has by its 

 very activity deprived itself of its source of nutrition and con- 

 sequently dies before it has established itself within its host. 

 Salmon (14) has shown in the case of plants immune to 



13. Ward, Marshall H. Recent Researches on the Parasitism of Fungi. 

 Ann. Bot. 19 : 154, 1905. 



14. Salmon, Ernest S. On Raising Strains of Plants Resistant to Fun- 

 gous Disease. Roj-. Kort. Soc. Rept. 3rd Inter. Conf. on Genetics 

 1906 : 378-384, 1907- 



