Stinking Snint or Bunt i>i W/ieai. 



73 



wheat is followed, the smut spores in the soil will have germinated and died, 

 and if two years are allowed to elapse before wheat is again sown the chances 

 are entirely against any smut spores having survived. Even the smut-balls 

 would be broken up by that time in the ordinary operations of working the soil, 

 or even by the slow movement of water in the soil. An experiment bearing 

 on this was carried out with unbroken smut-balls in the soil to see if the 

 spores were disturbed. Clean seed wheat was planted by hand in two rows 

 alongside each other, in one of which the seed was pickled with bluestone 

 and the other not, and unbroken smut-balls were planted close to the grains 

 in each row. The result was that the plants were all clean in the pickled 

 row, while in the unpickled several plants were bunted, thus showing that 

 the smut-balls in the soil, even when undisturbed by the plough, can infect 

 the seed wheat when not pickled. 



Infection. 



The mode of infection has been investigated, among others, by Kuehn^ 

 who artificially infected the youngest seedling stage with the spores, and 

 afterwards traced the course of the germ-tubes by means of sections. He 

 found that both primary and secondary conidia were capable of infection, 

 and that the germ-tubes penetrate the epidermal cells directly through the 

 walls, always in the neighbourhood of the lowest node. Just as the young 

 seedling emerges from the grain, it is then in the most susceptible condition, 

 and it may be attacked at any point up to the first joint, which is sometimes 

 called the tillering point. The first joint is always beneath the surface of 

 the soil, when the grain is drilled or harrowed, and not lying on the surface 

 of the ground. Above that the plant cannot be infected, because the cuticle 

 is too tough to allow the penetration of the delicate germ-tube. Therefore, 

 unless the bunt spores were sown with the seed or existed in the soil, there 

 is no possibility of infection. Once the germ-tube has entered the young 

 seedling a mycelium is formed, which, if it reaches the growing point, keeps 

 pace with the lengthening plant, chiefly growing among the loose cells of 

 the pith, without interfering to any perceptible extent with the healthy 

 growth of the plant, and finally reaching the ovaries, where spores are formed. 

 It is thus seen how the parasite has conquered the host-plant in the long run, 

 for just at the critical time, when the wheat plant is about to store away in the 

 ovary for the benefit of the young embryo all the valuable materials accumu- 

 lated during the growing period, the fungus enters in and appropriates 

 them, rapidly growing at their expense, and forming a network of delicate 

 branching hyphcB, which give rise to the innumerable dark-coloured spores. 



Since infection only occurs in the young seedling by means of spores 

 attached to the seed or by spores derived from smut-balls in the soil adjoining 

 the seed, and since these spores are known to be destroyed or their germination 

 prevented by bluestone solution, formalin, or hot water, the reason for 

 steeping the seed before sowing is evident, while at the same time it is not 

 seriously affected by the solution employed, particularly the two latter. 



Artificial Infection of Seed. 



Since a number of the plots were artificially infected, and as it is the usual 

 way of testing susceptibility to the disease, it seemed desirable to see if 

 dift'erent results were obtained, according as the spores were applied wet or 

 dry and in larger or smaller quantities to the seed. The Wallace variety 

 of wheat was chosen, and one plot was sown without infection as a check, 

 while another was infected and treated with bluestone for comparison! 

 When applied wet the spores wore made into a paste with water, and the 



