Jan ao, 1923 
Cytological Study of Infection 
149 
SUMMARY 
The germination of the spores and the formation of the appressoria on 
the stomata take place in the same way in the susceptible and immune 
hosts. 
In Baart the fungus enters freely and grows rapidly. In Kanred, under 
greenhouse conditions, only a few of the fungi pass through the stomata; 
the rest remain outside until they shrivel and die. 
In a congenial host, numerous haustoria are formed. A slender- 
growing hypha strikes a host cell, swells at the tip, its pair of nuclei 
divide, and a septum is formed, marking off a short terminal cell. This 
haustorium mother cell is closely appressed to the host cell, forms a fine 
pore through its wall and the host wall, and its contents, including both 
the nuclei, which have decreased in size, and the cytoplasm, now pass in, 
forming the haustorium. The osmotic membrane of the host appears to 
be invaginated by the haustorium, but apparently is still intact. 
In Kanred the process is similar until a small haustorium is formed, 
which, either by its presence, or, as is more likely, by secreting some sub¬ 
stance in the host cell, sets up chemical reactions within that cell, causing 
its collapse and death. The further diffusion of toxic substances into 
healthy host tissues is checked by the formation of thickened contact walls. 
One or more of the substances formed in the host cell diffuse into the 
haustorium, killing it, and causing collapse of the mother cell and the 
death and plasmolysis of the hypha back of it for some distance. If this 
reaction is rapid, the haustorium is destroyed while still very small; if 
more sluggish, a full-grown haustorium may be formed and some nourish¬ 
ment for further growth be extracted by the fungus. 
Kanred possesses three means of defense against this strain of stemrust; 
stomata which shut out the majority of the fungi, the heavy contact walls 
adjoining pathological cells, and a true immunity. The observations 
recorded here are in line with the theory that immunity is due to definite 
antagonistic chemical interactions between host and parasite. 
LITERATURE CITED 
(1) Allen, Ruth F. 
1921. resistance to stemrust in kanred wheat. In Science, n. s., v. 53, 
no. 1382, p. 575-576. (Preliminary report.) 
(2) Bary, A. de. 
1867. nEue untersuchungEn Ober urEdineen. In Monatsber. K. Preuss. 
Akad. Wiss. Berlin, 1866, p. 205-215, 1 pi. 
(3) Biffen, R. H. 
1907-12. STUDIES IN THE INHERITANCE OF DISEASE-RESISTANCE. In Jour. 
Agr. Sci., v. 2, pt. 2, p. 109-128; v. 4, pt. 4, p. 421-429. 
(4) Blackman, Vernon H. 
1904. ON THE FERTILIZATION, ALTERNATION OF GENERATIONS, AND GENERAL 
cytology OF the urEdtnEae. In Ann. Bot., v. 18, no. 71, p. 323- 
373, pi. 21-24. List of papers, p. 368-369. 
(5) Butler, E. J. 
1918. immunity and disease in plants. In Agr. Jour. India, 1918, Spec. 
Indian Sci. Cong. No., p. 10-28. 
(6) Call, L. E-, and Salmon, S. C. 
1918. growing wheat in Kansas. Kans. Agr. Exp. Sta. Bui. 219, 51 p., 
11 fig. 
(7) Eriksson, Jakob. 
1897. VIE LATENTE ET PLASMATIQUE de CERTAINES URtjDINtCES. In Compt. 
Rend. Acad. Sci. [Paris], t. 124, no. 8, p. 475-477. 
