52 



most dangerous of all. Even in midwinter with very great cold they rarely 

 freeze ; it might be when it has rained the day before." On pages 420 and 

 500, he says of api)le and pear trees that "an excess of fatty, oily fertilizers 

 easily develops blight and canker," i. e. creates a predisposition. 



The third one of the books published in 1795, the one by Rittcr v. Khren- 

 fels' is even more specialized, for he treats only of fruit trees. He 

 declares that all kinds of trees would be subject to blight and that "this decay 

 which appears first in the bark and then in the wood" is the most common 

 disease of trees and in some books is termed canker. The description which he 

 gives is so clear that it can be identified as the phenomenon now known as 

 iVectria-canker. He says, "the indication of this evil attack is first of all a 

 black or blackish bark which, six or eight days after its appearance, is often 

 pushed out, forms little splits and gradually loses its connection with the 

 trunk of the tree so that it clings only loosely to the shaft. After some time 

 the loose bark is entirely separated from the trunk and exposes the wood. 

 In this new stage the vitality of the '^ick plant docs its very licst to help itself 

 and unceasingly throws off the unfa\oral)lc or sick parts, but this vitality 

 finally becomes weakened and the tree dies. The tree attempts to form a 

 new bark which grows in folds more or less overlapping and tries to cover 

 the exposed places" .... He ascribed the cause to injuries as, for 

 example, from injudicious pruning, injuries due to insects and the like, "even 

 at times the tendency to blight lies in the disposition of the tree itself, — a 

 disposition which the trees obtain from the soil in wliich thev grow, from 

 (heir descent and from an unwise cultivation." 



In the pomological glossary published at the beginning of the la.st cen- 

 tury, Christ- added to the above by the further statement, that the blight 

 "often is due to freezing in winter." 



Burdach'' also bases his statements on his own observations and 

 says of blight, "this disease is an indirect result of weakness and commonly 

 arises in those trees whose growth has been hastened by strong forcing and 

 fertilizing or which have been transplanted to a poor garden soil where only 

 the upper part of the ground has been improved. In cherry trees, still an- 

 other evil effect arises from the same cause, viz. the exudation of resin or 

 gum." 



The theory of the inHucncc of llie soil and fertilization, as among the 

 most important causes of plant diseases, is now laid aside for some time and 

 attention is given to the manifold and extensive investigation of the province 

 of fungus life. 



Although anli(juity had already recognized a number of edible and 

 poisonous fungi, yet their attentive observation and systematic study began 



1 Ritter v. Ehrenfels, Ueber die Krankheiten und Verletzunsen der Frurht- 

 und Gartenbiiume. Bresslau, Hirshberg und Lissa 1795. 



2 Pomologisches theoretisch-praktisches Handworterbuch. Leipzig 1802. 



3 Systematisches Handbuch der Obstbaumkrankheiten. Berlin 1§18, 



