PARASITISM AND RESISTANCE 395 



nutrients for Puccinia graminis tritici, and the white pine and Ribes for 

 Cronartium ribicola, or that the nutrient requirements of the haploid 

 mycelium are different from those of the diploid mycelium. 



Much more investigation is needed to increase our knowledge of possi- 

 ble correlations between pathogenicity and metabolic products. This 

 should lead to a better understanding of parasitism. The possible role 

 of antibiotics occurring naturally in host plants as a factor in disease 

 resistance has received some attention recently, but much more knowl- 

 edge of this type is desired. Many of the problems of today may come 

 nearer to solution with a clearer understanding of the enzyme systems of 

 the parasitic fungi and the basic principles of specific enzymatic action. 



REFERENCES 



Allen, R. F.: Cytological studies of infection of Baart, Kanred and Mindum wheats 



by Puccinia graminis tritici forms III and XIX, Jour. Agr. Research 26 : 571-604, 



1923. 

 Allen, R. F.: A cytological study of Puccinia triticina physiologic form 11 on Little 



Club Wheat, Jour. Agr. Research 33: 201-222, 1926. 

 ♦Arthur, J. C, F. D. Kern, C. R. Orton, F. D. Fromme, H. S. Jackson, E. B. 



Mains, and G. R. Bisby: The Plant Rusts, John Wiley & Sons, Inc., New York, 



1929. 

 Bessey, E. a.: a Textbook of Mycology, The Blakiston Company, Philadelphia, 



1935. 

 Boyle, A. M.: Further studies of the bacterial necrosis of the giant cactus, Phyto- 

 pathology 39 : 1029-1052, 1949. 

 *Brooks, F. T.: Host resistance to fungi, chiefly in relation to obUgate parasites, 



Proc. Roy. Sac. (London), Ser. B, 135: 180-186, 1948. 

 Brown, W.: Studies in the physiology of parasitism. I. The action of Botrytis 



cinerea, Ann. Botany 29: 313-348, 1915. 

 Brown, W.: Studies in the physiology of parasitism. VHI. On the exosmosis of 



nutrient substances from the host tissues into the infection drop, Ann. Botany 



36: 101-119, 1922. 

 •*Brown, W.: The physiology of the host-parasite relation, Botan. Rev. 2: 236-281, 



1936. 

 Brown, W.: Physiology of the facultative type of parasite, Proc. Roy. Soc. (London), 



Ser. B, 135: 171-179, 1948. 

 Butler, E. J.: Immunity and disease in plants, Agr. Jour. India, Special Indian 



Sci. Congr. Issue, 1918 : 10-28. 

 Caldwell, R. M., and G. M. Stone: Relation of stomatal function of wheat to 



invasion and infection by leaf rust (Puccinia triticina), Jour. Agr. Research 52: 



917-932, 1936. 

 *Chona, B. L. : Studies in the physiology of parasitism. XIII. An analysis of factors 



underlying specialization of parasitism, with special reference to certain fungi 



parasitic on apple and potato, Ann. Botany 46: 1033-1050, 1932. 

 CoNANT, N. F., D. S. Martin, D. T. Smith, R. D. Baker, and J. M. Callaway: 



Manual of Clinical Mycology, W. B. Saunders Company, Philadelphia, 1944. 

 Cook, M. T., and J. J. Taubenhaus: The relation of parasitic fungi to the contents 



of the cells of the host plants, Delaware Agr. Expt. Sta. Bull. 91, 1911. 



