Stijikiiig Smut or Binii in }\']icat. 85 



growth ill order that the germ-tube of the fungus may penetrate, and this 

 period is of very short duration. Next, the germ-tube must grow and reach 

 the growing point, or it would not be able to develop and produce the disease. 

 But a main reason for some plants being attacked and others not lies in the 

 fact that there are certain substances known as chemotactic substances in 

 the plant which favour the entrance of the germ-tube of the fungus and its 

 development inside. There are also substances which actually repel the 

 germ-tubes, and it is the presence or absence of these substances which deter- 

 mines whether an individual plant will be attacked or escape. The seed 

 from plants, however, which escaped infection in one season have been 

 sown the next and found to succumb. 



11. Why are some iilants fartially hunted — only some of the ears being 

 affected and not all ? 



It often happens that only the secondary or late ears are affected, the 



others being clean, and this might arise from the fungus filaments at the 



base of the plant only reaching the growing point of the slow and late 



developing plants, while the others escaped. In other cases, where the 

 fully developed ears were bunted, the germ-tube had evidently reached the 



growing point of the seedling, and the mycelium had kept pace with, the 

 growing plant. 



12. Why are some ears only partially bunted ? 



Under ordinary conditions the whole of the grains in an ear are affected, 

 but in certain seasons it is not unusual to find ears in which some of the 

 grains are bunted and others clean (Plate II., B). It may be that 

 one side of the ear has escaped, but usually the sound grains are interspersed 

 among the bunted. In one particular case the lower grains were all bunted, 

 then about the middle an occasional one was clean, and at the top both 

 smutted and sound occurred, the topmost grain, however, being diseased 

 (Plate II., C). The normal condition is that all the grains in an ear are 

 attacked, and when some escape it can only be owing to the spore-bearing 

 hyphae failinu; to reach these particular grains. It might be thought that 

 the grains -which escape the invasion of the fungu.s to form spores had some 

 resisting power, but when the clean grains in a partially bunted ear were 

 infected and sown they produced bunty plants, showing that there was 

 nothing in the grain itself to account for its escape. 



13. Why are some grains of ivheat only partially bunted ? 



This was a comparatively rare occurrence, only appearing in one ear 

 of the variety known as Cedar, grown at Dookie, and in one ear of Genoa, 

 grown at Burnley. In the latter ear there was only one grain partially 

 bunted, three entirely bunted, and all the rest free. In the partially bunted 

 grain the fungus had evidently exhausted itself in producing its spores only 

 on one side, and why the whole of the starch w^as not utiUzed, as is usually 

 the case, in the formation of spores, might be due to the slow growth of the 

 fungus, or its late entrance into the grain, as evidenced by the embryo having 

 had time to develop. 



In fact, in all these cases, whether it is smutted and sound plants on the 

 same stool, or smutted and sound grains in the same ear, or even when the 

 grains are only partially smutted, the probable explanation is the same, that 

 by some accident of growth the fungus did not undergo its full development, 

 and was unable to reach all parts of the plant as usual. 



