RUST-RESISTANT VARIETIES OF WHEAT 41 



the other hand Errera (1892, p. 373) contends that so-called chemotro- 

 pism is in many cases merely positive or negative hydrotropism. Ful- 

 ton (1906, pp. 81-107) says that there is no definite chemotropic re- 

 sponse on the part of fungi. Nutrient solutions cause marked growth, 

 in his opinion, but cause no definite turning of hyphae in their direc- 

 tion. Hydrotropism, however, was observable. 



The behavior of the germ tube of Puccinia graminis and its en- 

 trance into the host plant has been described and figured by various 

 authors. Ward (1881-1, p. 217) figures it as forming a slight swell- 

 ing and then growing directly into the tissues 'of the host. Bolley 

 ( 1889, p. 14) shows the germ tube growing directly through the stom- 

 atal opening and branching out between the mesophyll cells. This has 

 never been seen by the writer. An appressorium always formed in all 

 cases of infection observed. Pole Evans (1907, p. 445) describes and 

 figures normal infection quite completely. 



A considerable amount of work has also been done on determining 

 the fate of germ tubes when they are produced on immune host plants. 

 Klebahn noted (1896, p. 263) that sporidia of Puccinia convallariae- 

 digraphidis could bore through the epidermal walls of Polygonatum 

 multifiorum, an uncongenial host, but that the germ tubes developed no 

 further. He concludes that infection is of the nature of a conflict be- 

 tween host and parasite. Ward (1901 and 1902) showed in connection 

 with Puccinia dispersa on bromes that the germ tube might enter and 

 cause normal infection, the mycelium might develop and never produce 

 pustules, or the tissues of the host plant might be killed very early, 

 thus precluding the possibility of much development on the part of 

 the fungus. The same author further shows (1904, p. 29) that in 

 normal infection of a susceptible species of Bromus the host cells 

 retain life for a surprisingly long time. Miss Gibson (1904) examined 

 the leaves of a large number of plants, widely separated taxonomically, 

 which had been inoculated with spores of I] redo chrysanthemi. She 

 found that the germ tubes might enter the plant tissues very readily 

 but never formed any haustoria and consequently no pustules. 

 Furthermore the hyphae usually died when t^ey came in contact with 

 a cell. On resistant varieties of Chrysanthemum it was found that 

 haustoria might develop, but areas of host tissue in the neighborhood 

 of the hyphae were killed, thus preventing the further spread of the 

 fungous mycelium. Her conclusion is to the effect that when the 

 germ tube of a uredine fungus enters any but its proper host plant a 

 struggle goes on, resulting in the death of the host locally and of the 

 parasite. The closer the relationship between the plant and the proper 

 host of the rust the longer and more extensive will be the struggle. 

 Salmon (1905) found that when barley was inoculated with spores 

 of Erysiphe graminis from wheat incipient haustoria might be formed 



