55 



The literature now begins to be increased by single works, scientific as 

 well as practical manuals and writings on both agriculture and horticulture 

 which treat of diseases (Tessier, Jager, Hopkirk, the text books of Willde- 

 now, Nees, de CandoUe, Wenderoth, Reichenbach, Re and Kieser) to such 

 an extent that we can now emphasize only those publications which deal most 

 fully with the history of pathology. 



Among these belong primarily F. Unger's^ "Exantheme der Piianzen" 

 published in 1833 and giving the results of the most industrious 

 and conscientious studies. This physician, living in a small isolated Alpine 

 valley, supplements his observations by many very careful original drawings, 

 true to nature, on which he constructs his theory of disease. "Most plant 

 diseases are located in the juices .... The faulty formation and the 

 numerous abnormalities in the chemical process of the nutritive juice as well 

 as similar faults in the more highly active life-sap, are the causes of innumer- 

 able diseases which become evident in a scanty formation of the plant sub- 

 stance, the accumulation of excretory substances, the breaking up of the 

 parenchyma, the changed constitution of the secretions etc., or by conditions 

 of an opposite character. In every case, most of the quantitatively and quali- 

 tatively changed processes of the vegetative "chylopoese" might be taken 

 as the source of diseases which may be recognized from the change in sub- 

 stance rather than from that of form. The position into which a large 

 number of the plants are transplanted often acts so detrimentally upon them 

 that at least the greater part deserve to be called diseased." 



Although, according to this presentation, we must suppose on the whole 

 that Unger would consider diseases as functional and formal variations in 

 the life-history of the organism, he, nevertheless, arrives at the conclusion 

 that disease is something foreign. "For just as the cosmic and elementary is 

 related to the organic, child-like, antitypical, as something parental or typical, 

 in the same way the organism is related to the disease tvhich is nothing else 

 than a second lozuer organism whose elements already lie hidden in some 

 other higher one." In this theory lies the continuation of the thought ex- 

 pressed by Batsch on the nature of the parasitic organisms. 



Unger states that "among the plant diseases least betraying any depen- 

 dence upon the organism attacked and which in their root formations are 

 still so intimately interwoven with this organism, there belong indisputably 

 those forms which we designate by etiolation, dropsy (anasarca), jaundice 

 (icterus), tympanitis, tabescence (tabes), failure of crops, proflu via and others. 

 Ihese form in fact by far the majority. Greater independence is shown by 

 the vast army of malformations, at the basis of which always lie deficiencies 

 in the amount of sap and therefore a retardation in lower developmental 

 stages. Honey-dew (Saccharogensis diabetica) is more important than these. 

 Its pathological course was first recognized by L. Treviranus and its more 

 universal significance by Dr. H. Schmidt. Mildew is indisputably related to 



1 Die Exantheme der Pflanzen und einige mit diesen verwandte Krankheiten 

 der Gewachse. Wein 1833. 



