IOWA ACADEMY OF SCIENCES. 



DISEASES OF PLANTS AND INSECTS. 



83 



In this lenprthy sketcli on pathosrenic germs the relations to hygiene have 

 been touched on sufficiently. I have not discussed many of the diseases, but with 

 such a vast subject, it is impossible to do so. Before I proceed to discuss the uses 

 of bacteria to agriculture, let me briefly refer to a few of the diseases they cause 

 in plants. Scarcely a decade ago DeBary,*^ Hartig*' and other phytopathologists 

 believed that the acid reaction of higher plants was detrimental to the growth of 

 bacteria in living tissues. Since then it has been shown that many bacteria find 

 acid media an excellent medium; moreover European, but more especially Ameri- 

 can investigations have shown that quite a number of plant diseases are caused 

 by these minute organisms. The pioneer work in fact in this direction was 

 paved by Americans. Most European authors like Kramer** and other bacteri- 

 ologists scarcely enumerate the work done by Americans. 



The only writers who have fully comprehended the subject are Ludwig of 

 Greiz,*' and Comes''^ of Itu.ly, yet more than a decade ago Professor BurrilP' 

 worked out the causal relation between pear blight and Bacillus ami/lororm. This 

 was soon followed by the work of Prof. Arthur** on the same disease, and finally 

 some excellent work by Waite. Then followed the investigation of Hurrill'*'-' on 

 sorghum blight, the work of Kellerman and Swingle"' on the same disease. 

 Tuberculosis of the olive by Savastano", blight in oats by Prof. Galloway^- and 

 Wakker's^' Yellows of Hyacinths has become quite familiar to phytopathologists 

 of Europe. 



It has been demonstrated that there are other plant diseases caused by micro- 

 organisms. These have been tabulated in an interesting paper by Dr. RusselP*. 



Not the least value may be expected from the part that micro-organisms play 

 in causing diseases of insects. Flacherie of the silkworm (Streptococcus bombi/cis) 

 long ago studied by Bechamp'^ and Pebrine [Nosema homhycis) discoveied by 

 Cornalia and carefully studied by Pasteur anu Naegeli are the oldest among 

 the known diseases caused by bacteria. Both are most troublesome enemies of 

 silk culture. Pasteur rendered this industry most important aids in suggesting 

 the separation of the moths m pairs in isolated numbered cells, and a microscopical 

 examination of the mates after they had deposited their eggs. The eggs from 

 diseased insects are not to be used for breeding purposes. Whether this organism 

 is to be classed with Bacteria or is one of the Sporozoa is still undetermined. 

 Metchnikoff classifies it with Sporozoa. 



Foul brood of bees, a most troublesome disease in the apiarj-, is caused by Bacillus 



»■- Lectures on Bacteria, 1S87. 



83Lehrbuch der Baumkrankheiten. 



8iDle Bakteriologie in lliren Beziehungen zur Landwirtschaft und den Landw, 

 Technlschen Gewerben. Pt. I, pp. 171. Pt. II, pp. 178. Carl Gerold's Sohn Vienna. 

 1890-1892. 



85Lehrbuch der niederen Kryptogamen, 1892. 



88Annual Report New York State Agr. Experiment Station, 1881, p. 357. 



89 Eighth Ann. Meeting See. Prom. Agrl. Sci., p. 30. 



90Annual Report Kansas Agr. Experiment Station, 1889. 



»iAnn. D. R. Scuola. Sup. d'Agri. in Portlci, Vol. V, fasc. IV, 1887. 



»2Journal of Mycology, vol. VI. 1890. 



93Bot. Centralblatt, Vol. XIV, 1883, p. 315. 



941. c. pp. 35-41. 



95Bechamp. : Compt rend., Vol. LXIV. 



Pasteur: Etudes sur les Maladies des vers a sole, Paris, 1870. 



Balblanl, Lecons, sur les Sporozoairies, Paris, 1884. 



