48 



influence of the dry spring winds, which scorch the foHage is worth noting: — 

 "The considerable quantity of moisture which is given off from the branches 

 of trees during the cold winter season, plainly shows the reason, why, in a 

 long series of cold, northeasterly winds, the blossoms and tender young set 

 fruit and leaves are so frequently blasted in the early spring, \\z. by having 

 the moisture exhaled faster than it can be supplied from the trees." 



DuhameP pays great attention to injuries from frost and states 

 that trees are often attacked by swellings which may be more easily healed in 

 younger than in older trees. At some place on the trunk, the bark is loosened 

 from the wood and a devouring pus occurs between the two. Devouring ab- 

 scesses of this kind are called "canker" which is counted among the diseases 

 j/roduced by a superfluity of sap. Das Xiedersachsische Gartenbuch- finds 

 the cause from blight and canker in too thick standing of the trees, in un- 

 favorable soil etc. 



While in ancient times and in the middle ages observations on plant dis- 

 eases were usually limited to a perception of the mature phenomena visible 

 to the naked eye and the solution of the questions of plant life were sought 

 almost entirely among experiments of budding, we find that the experiment 

 itself attained its own importance with Hales and Duhamel. 



Simultaneously with experimental physiology came the wider classifi- 

 cation of plant diseases. 



We follow here Seetzen's" treatment of the subject and its history. 

 Seetzen states that Tournefort had a finished* system*. His first class 

 includes the diseases due to internal causes, as opposed to the sec- 

 f)nd class, the diseases produced by external causes. To the first class he as- 

 cribes : — i-La trop grande abondance du ' sue nourricier ; 2-le defaut ou 

 manque de ce sue; 3-quelques mauvaises qualites qu'il pent acquerir; 4-la 

 distribution inegale dans les diflferentes parties des plantes. In the second 

 class belong: — i-La grele ; 2-la gelee ; 3-la moisissure: 4-les plantes, qui 

 naissent sur d'autres plantes ; 5-la piqueure des inscctes : Ti-dififerentes taillcs 

 ou incisions, que Ton fait aux plantes. 



We find T(~»urnefort's point of view in our modern systems. \\'e group 

 the diseases caused by excess or deficiency of water and food, with injuries 

 produced by weather extremes (frost, hail) etc. In the same way. we treat 

 wounds as a separate division. The parasitic diseases appear for the first 

 time as such in Tournefort's book. 



Less fortunate is Zwinger's" system which appeared shortly after 

 Tournefort's and which also is formed of two main groups, — (i) General 



1 La physique des arbres par Duhamel du Monceau. Pari.s 1758. p. 339. 



- Caspar Bechstedt. VolKstandises niedersachsiches Land- und Gartenbuch. 

 Flensburg und Leipzif? 1772. I, p. 151. 



■' Systematum g^enoraliorum de morbis plantarum brevis diiudicatio. Publico 

 examini submittit Ulricus .Jasper Seetzen. Gottingae MDCCLXXXIX. 



4 Observations sur les maladies des plantes par M. Tournefort. Mem. de I'Ac. 

 Roy. des Sciences a Paris 1705, p. 332. 



5 Jo. Jac. Zwingeri, Diss. med. inauguralis de valetudine plantarum fecunda et 

 adversa. Basileae 1708. 



