44 A STUDY IN CEREAL RUSTS 



the two. The fungus flourishes vigorously while for a considerable 

 length of time the host cells, even in the infected area, are apparently 

 quite healthy. In no case does there seem to be an extensive killing of 

 host tissue. 



INFECTION OF KHAPLI 



Spore germination of course occurs normally. The germ tubes 

 grow along the surface of the host epiderm cells in the same manner 

 as do those on Minnesota No. 163. The formation of appressoria 

 takes place in an entirely normal manner. The stimulus causing entry 

 into the stomatal slit is present, the method of entrance being sub- 

 stantially the same as in Minnesota No. 163. Apparently the vesicle 

 sometimes fails to send out infection threads but merely remains 

 directly beneath the stomatal slit and becomes vacuolated. It may send 

 out numerous, short, club-shaped branches all of which soon become 

 vacuolated and never send out any haustoria into the host cells. From 

 the beginning of growth in the host it is easily discernible that the 

 vigor of the hyphae is not nearly so great as is the case with those 

 growing in Minnesota No. 163. There is a greater tendency for the 

 tips of infection threads to round up, become vacuolated, and never 

 develop further. 



Fairly successful infection, however, may take place. Infection 

 threads may be sent out just under the epiderm or directly across the 

 substomatal space (see Plate VIII, 3 and 5). Haustoria, attached to 

 the hypha by delicate sterigmata, are sent into the cells and the hypha 

 grows fairly well. Sometimes many incipient infection threads are 

 formed from a single vesicle, only one developing (Plate VIII, 5). 

 Shortly after infection threads are sent out the vesicle usually dies. 



The infection threads are not always successful in sending 

 haustoria into the host cells. When the hypha comes into contact 

 with the cells the protoplast of the latter often shrinks back from the 

 wall, the nucleus shows definite signs of disintegration, the chloroplasts 

 are apparently lost, and the entire cell dies. The hypha may die also, 

 or it may grow and kill other cells. However, it usually eventually 

 succumbs. Typical examples of this will be seen on Plate VIII, 6 and 

 7. It will be noticed that at 6 the cell on which the hypha is abutting 

 is apparently dead, the chloroplasts have disappeared, and the nucleus 

 is disintegrating. At 7 this has taken place in only a part of the cell. 

 It sometimes happens that one branch of a hypha is fairly successful 

 while another may never develop to any extent at all. 



Whether or not the host cells are killed within a short time after 

 the hyphae come in contact with them, infection does not appear to 

 be normal. The hyphae may grow fairly well, but never as vigorously 

 as in Minnesota No. 163. Haustoria may be sent out in fair abundance 



