Flag Siiiiii of }Vhcat. 97 



that infection may arise from the soil, as well as from spores sown with the 

 seed. By treating the seed dusted with spores with hot water, for instance, 

 the development of Fla^ smut has been prevented, and the artificially in- 

 fected grains p-oduced healthy plants, but then the seed was sown in soil free 

 from it. It was at first difficult to understand how the spores were able to 

 infect the young seedling when they were not in contact with the grain, or had 

 their germinating power destroyed by various re-agents. But, since the 

 spores are capable of germinating in the soil and producing their elongated 

 conidia, these conidia can in turn put forth a long tapering germ-tube, which 

 may eventually reach the young plantlet as it emerges from the seed, or the 

 young shoots formed beneath the surface. 



Experiments in the infection of wheat with the spores of Urocystis tritici 

 have also been carried out by Hori^ in Japan. The spores were mixed with 

 the moistened grains before sowing, and as the result of two years' experi- 

 ments, while the uninfected seed produced clean plants, the infected seed pro- 

 duced both smutted and healthy plants in the ratio of 3 : 2. The conclusion 

 come to is as follows : — " These two years' experiments decidedly proved that 

 the smut is produced by the spores of Urocystis occulta \U . tritici] adhering to 

 the seed coat, whither they have been carried by careless thrashing. But it 

 may be possible, to some extent, that the matured spores, being easily scat- 

 tered by winds, could also reach the inner side of the flowers, and this may be 

 kept until thrashing time." The same investigator ^ also states that during 

 a period of five years he tried many experiments to test whether spores in the 

 soil iufsct the host. No details are given, only the general results. " After 

 thoroughly mixing the spores with the soil, seeds of the wheat were sown in 

 different intervals, partly on the same day, partly after five and ten days. 

 But the results were always negative, and no difference with the control plants 

 was noticed." In our experiments, as already shown, when diseased straw 

 was mixed with the soil in pots, there was invariably a crop of more or less 

 infected plants, while the control plants were clean. And not only so, but 

 in one case at least the infection was much more virulent from diseased straw 

 in the soil than from dusting the spores on the seed. It may be that suffi- 

 cient moisture is necessary to decompose the straw, or at least to scatter the 

 spor3s before they can produce their full effects, and in the pot experiments 

 the plants were always well and regularly watered. 



The coiiclusions to be drawn from our experiments as regards infection 

 are — ■ 



1. Plants may be infected by coating the seed with spores. 



2. Plants are liable to infection if seed is sown in soil containing 



diseased straw of the previous crop. 



3. Plants may become infected if sown on soil containing manure 



from horses or cattle fed on diseased hay. 



But a fresh light has been thrown on the infection of rye, and the same 

 probably applies to wheat. By the experiments of Hecke, already recorded 

 in Chapter VI., it was there shown that the spore has not only the one chance 

 of infecting the primary or terminal bud, but also the numerous chances of 

 infecting the lateral buds produced beneath the surface of the soil and growing 

 out into fresh stalks. There is not only seedling infection, but shoot in- 

 fection, and it is decidedly to the advantage of the parasite to multiply the 

 points of attack as much as possible. This will explain how in an infected 

 soil the seed may be quite free from spores and disinfected, while the young 

 shoots are infected by the spores already in the soil. 



1858. E 



