53 



According to the earlier hypotheses, infection was dependent on the direct products of 

 germination of the smut spores: therefore, solo speak, on these alone. It was assumed from 

 llii- -weakly germinating smut scores that they inoculated the germinating seedlings and that 

 from these inoculations smutted plants were produced in our grain fields. This theory, however 

 short and convenient for the explanation of smut infection, has been supplemented by the proof 

 of an extensive distribution and propagation of the smut germs in saprophytic substrata outside 

 of the host plants. Only by determining this has the KWV. I'M which the germs of infection are 

 distributed, become clearly and certainly understood, as well as the natural infection and distri- 

 bution of smut germs as observed universally in nature. The biological section with the devel- 

 opment of smut fungi on saprophytic substrata outside the host plants, forms, according to our 

 present understanding, the complement of the section with development taking place in the host 

 plants. Both parts are now united in a harmonious whole and nothing can characterize this 

 harmonious union further and more sharply than the fact that, for instance, in the forms of\ 

 the genus Ustilago. at the time of parasitic life in the host plants, only chlamydospore fruit forms, 

 tlie typical smut spores, mature and that during the period of saprophytic nutrition only conidia 

 fruit forms appear. For this strict alternation in the maturing of the fruit forms which takes 

 place here, not, as in the case of the Uredineae, on two different hosts, but after saprophytic and 

 parasitic nutrition. TIT can for the present find no other explanation than the influence exer- 

 cised on the development of our plants, at one time by the living substrata, the next time 

 by the dead substrata. How would it be possible, according to the earlier conceptions and the 

 earlier knowledge which had not led even so far as to the germination of the smut spores, to 

 explain the phenomena in maize smut and to understand them correctly, if the portion of the 

 development of smut fungi enacted saprophytically did not furnish the natural explanation for 

 all details? It is scarcely possible to find anywhere in the whole domain of infectious diseases 

 a more complete or finer picture of this most striking phenomenon as it exists most clearly here 

 in the etiology of the maize smut. And not less clear has become the understanding of the 

 >mut forms living in our grains which propagate their germs of infection in the soil by sapro- 

 phytic nutrition and especially in manured soil, in such a way that infection* of the germinating 

 seedling may thereby be understood and the significance of manure for the occurrence of smut 

 diseases in grain as agriculturists have always emphasized is shown in the proper light. 



i i rtainly, however, the phenomena of blossom infection are not less convincing and clear. 

 In them the smut germs find their nutrient substrata in the secretion of the stigma and the 

 exudation of honey, which are as favorable as pqssible for germination, development and propa- 

 gation of the germs of infection. 



It took a long time, more than the lapse of twenty years, to make possible the obtaining 

 of the explanations here given concerning the biology of the smut fungi, their infection, the 

 phenomena of the disease and the natural distribution of smut fungi on saprophytic substrata. 

 It was not easy to find in the separate cases the right road which would lead to this goal. 



It should be noticed here, however, that ,the universal end of the new investigations, how- 

 ever successful they have proved to be in the cases already carried on, has not in any way been 

 reached and that still many separate experiments must be carried out in order to obtain the 



