198 Journal of Agricultural Research voi. iv. no. 3 



rapid action results in the almost immediate death of the host cells. 

 The degree of susceptibility is indicated to a certain extent by the rapid- 

 ity of this action. The more resistant a form, the quicker are a few host 

 cells in the immediate neighborhood of the invading hyphae killed and 

 the sooner does the fungus itself cease activity. The visual evidence 

 is clear, but the exact interpretation of the results is more difficult. 

 Marryat (5) considers that the hyphae of P. glumarum in an uncongenial 

 host starv^e on account of the death of the host cells. This may be the 

 correct explanation, but there seems to be a very definite antagonism 

 between the immune plant and the parasite, which may possibly require 

 another explanation. The work of Ward (9-12) on P. dispersa, of 

 Spinks (6) on P. glumarum, and of the writer (8) on P. graminis seems 

 to indicate that immunity and resistance, especially when very marked, 

 are quite independent of the nourishment of the plant, and although 

 this does not necessarily establish the case, it would seem to point to a 

 very fundamental antagonism. On the other hand, Comes (i) states 

 that resistance in wheats is due to the acidity of cell sap. It seems 

 clear, however, that plants nearly or quite immune to P. graminis ex- 

 hibit the same phenomena in more extreme form as do partially or 



highly resistant forms. 



SUMMARY 



(i) When plants practically immune to Puccinia graminis are inocu- 

 lated, the fungus gains entrance in a perfectly normal manner. 



(2) After entrance the fungus rapidly kills a limited number of the 

 plant cells. 



(3) The fungus, after having killed the host cells in its immediate 

 vicinity, seems unable to develop further. 



(4) The relations between plant and parasite in partially resistant 

 and almost totally immune plants are different in degree only. 



(5) Hypersensitiveness of the host seems to be a common phenome- 

 non not only among plants somewhat resistant to P. graminis but also 

 among those almost totally immune to it. 



LITERATURE CITED 

 (i) Comes, Orazio. 



1913. Delia resistenza dei frumenti alle ruggini stato attuale delta quistione e 



provvedimenti. In Atti R. 1st. Incoragg. Napoli, s. 6, v. 64, 1912, p. 

 421-441. Letteratura e note, p. 437-440. 



(2) Evans, I. B. Pole. 



1907. The cereal rusts. I. Development of their Uredo mycelia. In Ann. 

 Bot., V. 21, no. 84, p. 441-466, pi. 40-43. 



(3) Fromme, F. D. 



1914. Negative heliotropism of the urediniospore germ-tubes of Puccinia 



Rhamni. (Abstract.) In Phytopathology, v. 4, no. 6, p. 407-408. 



(4) Gibson, C. M. 



1904. Notes on infection experiments with various Uredineae. In New Phytol., 

 V. 3, no. 8, p. 184-191, pi. 5-6. 



