SOME BACTERIAL DISEASES OF PLANTS: THEIR 

 NATURE AND TREATMENT. 



BY PROF. H. H. WHETZEL, CORNELL UNIVERSITY. 

 ANNUAL LECTURE UNDER THE JOHN LEWIS RUSSELL BEQUEST. 



Delivered before the Society, with stereopticon illustrations, 

 March 9, 1907. 



Bacteria: Their Nature and Mode of Life 



Bacteria are now usually classed by scientists as plants. In the 

 popular mind they are, however, very generally regarded as ani- 

 mals. The ludicrous illustrations of these organisms in the patent 

 medicine advertisements of the newspapers are, perhaps, largely 

 responsible for this popular misconception. The lack of those 

 organs, such as stems, leaves, roots, etc., which we commonly 

 think of as parts of all plants, together with the fact that many 

 bacteria possess organs of locomotion or propulsion has influenced 

 the more intelligent of the laymen to class them, perhaps rather 

 unconsciously, with the animals. 



They are of all plants the smallest, some of them requiring the 

 very highest power of the modern microscope to make them 

 visible. The bacteria that cause the well known Fire Blight of 

 pears and apples are so small that if placed end to end it would 

 require 25,000 to span an inch auger hole. Although there are 

 hundreds of species of bacteria they are all very simple in form and 

 structure, being either globose, rod-shaped, or spiral. Those caus- 

 ing the diseases of plants have almost without exception the rod- 

 shape. In structure they are very simple, consisting of a single cell, 

 that is, a cellulose membrane or sac enclosing a living mass of pro- 

 toplasm. This living protoplasm is in general appearance not 

 greatly unlike the white of an egg. Their method of multiplication 



