378 The Study of Plant Diseases. 
Another field of research in which much work has recently been 
done is that of tracing other stages in the life-history of parasitic 
fungi which were originally classed as “ Fungi Imperfecti.” Many 
of these organisms are virulent agents of disease and it has been a 
matter of some importance to ascertain if any higher stage is present 
in the full cycle of development. Thus the common scab of Apple 
Trees, Fusicladium dendriticum, is now known to be the conidial stage 
of the ascomycetous fungus Venturia pomi. Similarly the fungus 
causing the brown rot of fruit and originally called Monilia 
fractigena, really belongs to the ascomycetous genus Sclerotinia. 
Considerable attention has recently been paid to the study of 
bacterial diseases of plants. A few years ago it was customary to 
doubt the existence of such diseases, partly on account of the fact 
that the cell-sap of the higher plants, possessing as it generally does 
an acid reaction, was thought to be inhibitive to the action of these 
organisms. This view has had to be modified in recent years and 
nowadays several well known diseases of plants are known to be 
induced by specific bacteria. Burrill in 1878 was the first to 
establish the existence of a definite bacterial disease, for in that 
year he showed that the Blight of Pear trees was due to a species 
of bacterium. 
Erwin F. Smith of the United States has determined the 
presence of distinct bacterial diseases of Potato, Cabbage, 
Cucumber, etc., and Potter, 1 in this country has identified a 
bacterial disease of Turnips. In the current number of Science 
Progress, Potter gives a useful summary of the general progress 
that has so far been made in the study of pathogenic bacteria 
affecting the higher plants. 
It may be of use at this juncture to say a few words about 
books dealing with plant diseases. The older continental books by 
Frank, 2 Sorauer, 3 Tubeuf, 1 Prillieux, 5 and others are still the most 
comprehensive although they do not deal with some of the diseases 
which have come into prominence during the last few years. Of 
Tubeuf’s book there is an excellent English translation by W. G. 
Smith. 6 In regard to the special diseases of trees R. Hartig’s book 
1 Potter. Proc. Roy. Soc., 1900. 
2 Frank. “ Die Krankheiten der Pflanzen.” 2nd edition. Breslau, 
1895. 
3 Sorauer. “ Handbuch der Pflanzenkrankheiten,” Berlin, 1886. 
* Tubeuf. “ Pflanzenkrankheiten durch Kryptogame Parasiten 
verursacht,” Berlin, 1895. 
6 Prillieux. j“ Maladies des plantes agricoles,” Paris, 1895. 
0 Tubeuf and Smith. “ Diseases of Plants induced by Crypto- 
gamic Parasites,” London, 1897. 
