INTRODUCTION 3 



been recognized how great is the importance for the welfare of 

 plants of the quantity and condition of the mineral matter in 

 the soil, and how an irrational treatment of the soil, such as 

 scourging the ground, in sylviculture, agriculture, and horticulture 

 can and must lead to exhaustion of one or other of the nutritive 

 ingredients, which betrays itself in the stunted growth of the 

 crop, it was supposed to be permissible, though unsupported by 

 any exact investigations, to proceed a step further, and to regard 

 acute diseases of crops, so long as they could not be ascribed 

 to external causes, as the results of the want of one or other of 

 the nutritive substances of the soil. The fact that unhealthy 

 symptoms make their appearance quite as often on very fertile 

 soils as on poor ones led to the assumption that a superfluity 

 of nourishment may also be the means of causing diseases in 

 plants. 



The works of De Bary 1 and Tulasne 2 first opened the way 

 for the investigation of plant-diseases ; and with the appearance 

 of these a new period began, for from that time onwards very 

 great attention has been devoted to the life-history and action 

 of parasitic fungi. The view hitherto held that all fungoid 

 growths appear only as the result of previously existing pro- 

 cesses of disease, or as indications of the incipient death of the 

 part of the plant which is attacked, was shown to be erroneous. 



Investigation was now directed chiefly to the diseases of 

 farm and garden crops. Amongst others Jul. Kiihn 3 especially 

 enriched science by a series of most valuable investigations. 

 Further research gained a surer basis with the appearance of 

 de Bary's 4 Morphology and Physiology of the Fungi. 



So far the attention of investigators had been almost entirely 

 directed to agricultural crops, a circumstance which is sufficiently 

 explained by the fact that but few scientific botanists had the 

 opportunity presented to them of carrying their researches into 



1 De Bary, Untersuchungen iiber die Brandpilze und die durch sie veran- 

 lassten Krankheiten der Pflanzen mit Riicksicht auf das Getreide und andere 

 Nahrpflanzen. Berlin, 1853., 



2 Tulasne, Selecta fungorum carpologia. Paris, 1 86 1. 



3 Julius Kiihn, Die Krankheiten der Ctdturgeivcichse, ihre Ursachen und 

 Verhiitung. Berlin, 1858. 



4 De Bary, Morphologie und Physiologie der Pilze, &c. Leipzig, 1866. 

 and Vergleichende Morphologie und Biologie der Pilze. Leipzig, 1884. 



B 2 



