54 



results made possible by this newly acquired understanding of the matter. The investigations are 

 therefore as difficult as they are wearisome and experimental infection encounters impediments 

 in the undertaking and in its carrying out which are scarcely imaginable in advance. 



The peculiarity of these experiments on infectious diseases in plants is that they can be 

 carried out in part only with the resources of an institution ; and in part, moreover, only with 

 those of an experimental field in which the cultures of inoculated plants must be brought to a 

 finish. The undisturbed harmonious co-operation of these two factors, the arranging of the 

 experimental field, the preparation and the work in the institution, is possible only if the experi- 

 mental field and the work rooms of the institute are as closely and conveniently connected as pos- 

 sible. Only thus is it possible to observe the cultures for any length of time and to keep away 

 the many kinds of external disturbances to which they are exposed in the course of the period 

 of growth. 



The chief impediment to the rapid progress of investigations and experiments in this 

 direction lies, however, in the circumstance that, during the whole length of time of one growing 

 period, experiments can be made only once, the results of which are given only at the end of the 

 summer. If these experiments have been disturbed by secondary and other injuries, or if they 

 give only negative results, a whole year is lost be fore the experiments can be renewed and supple- 

 mented. Thus several periods of growth are often needed for the deciding of simple questions 

 and the end of the experiments can be reached only years later, by the dispatching of questions, 

 possible only from time to time. In this way it becomes obvious that the investigations reported 

 here have not been absolute, even in the most favorable cases, but are only relatively conclusive. 

 In many places, the points in question have been left open where the results already obtained 

 from the cultures have not been sufficiently decisive. Years must still elapse before one can 

 speak of universally conclusive results. 



If one considers this state of affairs and the unusual circumstances which come into con- 

 sideration in the experiments and their carrying out, one will involuntarily be led to think that 

 an arrangement suitable for the investigation of smut diseases and similar infectious diseases 

 would be most opportune. If only the damages which are annually caused by the smut of grain 

 be compared with the expenses of an institution of the kind indicated, this small material sacrifice 

 would certainly not be proportionate to the prospective advantages of an explanation of the 

 natural spread of smut diseases and the successful struggle against them. But here the external 

 resources of an institution and of the experimental field are not primarily concerned. Even if 

 these are granted no favorable results can be obtained when there does not lie at the disposal of 

 the management of such an institution a power broadly educated in the understanding of the 

 matter and also mycologically. 



