2 DISEASES OF TREES 



bound to be defective in accordance with the position of 

 botanical science at that time. 



Some fifty years ago a number of able investigators, of whom 

 only Saxesen, Th. Hartig, and Ratzeburg need be named here, 

 applied themselves to the study of insects. The life -history of 

 forest insects, their harmfulness or usefulness, soon became the 

 favourite study of many practical foresters, and in a few decades 

 the joint efforts of numerous workers were rewarded by the 

 elevation of Forest Entomology to the position of a much- 

 appreciated subject of scientific instruction, which has become 

 the common property of all educated foresters. 



The case was otherwise with those plant-diseases which 

 cannot be ascribed to the injuries of animals. Their investi- 

 gation was delayed until quite recently ; for it was only after 

 botanical science, by the aid of its chief instrument, the 

 microscope, had obtained a clear insight into the normal struc- 

 ture and vital phenomena of plants, and especially after the 

 study of fungi had been prosecuted in the last few decades by a 

 series of distinguished investigators, that the examination of the 

 phenomena of disease in the life of plants could be undertaken 

 with a prospect of success. 



During the period from 1833 to 1841 three text-books of 

 plant-diseases did indeed appear namely, those of Fr. Unger, 1 

 Wiegmann, 2 and Meyen 3 which bear witness that in attempt- 

 ing to explain the phenomena of disease in plants the progress 

 already made in the knowledge of the structure and life of 

 plants was not left out of account ; but the erroneous views as to 

 the nature of fungi, and the absolute ignorance of the history 

 of their development which prevailed, impeded progress towards 

 a clear understanding of the processes of disease. Independent 

 investigation was especially interfered with by the mistaken 

 attempt to apply to the study of the diseases of plants the 

 scientific results which J. von Liebig in particular had obtained 

 in the department of agricultural chemistry. After it had 



1 Fr. Unger, Die Exantheme der Pflanzen und einige mit die sen verwandte 

 Krankheiten der Gewachse. Vienna, 1833. 



2 Wiegmann, Die Krankheiten und krankhaften Missbildungen der 

 Gewachse. Brunswick, 1839. 



3 Meyen, Pflanzenpathologie. Lehre von dem krankhaften Leben und 

 Bilden der Pflanzen. Berlin, 1841. 



