Progvess of Botany. 51 



as by a sincere desire to get at the truth. The researches 

 and speculations to which his book gave birth imparted a 

 mighty influence to the study of all forms of life. One 

 immediate result was that greater attention than they 

 had hitherto received began to be bestowed, on the beings 

 lowest in the scale. In consequence, the methods of 

 botanical study have been revolutionized. The microscope 

 plays now the leading part in every botanical laboratory ; 

 and evolution has proved a good working theory. Eecent 

 treatises on Botany begin with the study of embryology, 

 dealing with the simplest forms of plant life, and work 

 upwards to the most complex. Whatever one's views of 

 evolution may be, this is clearly the most advantageous 

 as well as most philosophical starting point for the student. 

 The researches of the last forty years have brought to 

 light innumerable forms of minute vegetable organisms. 

 Of diatomacea?, for instance, there were known only about 

 fifty species in 1800, — now four thousand at least have 

 been differentiated on the Continent of Europe alone. A 

 new world of fungal species, called bacteria, has been dis- 

 covered, and in some of these mankind has a serious 

 interest. That fell disease consumption is now known, 

 since Koch traced it in 1882, to originate in the ravages 

 of a fungus in the lungs, — bacillus tuberculosis. Pasteur 

 diagnosed the malady Hydrophobia, tracing it also to a 

 bacillus. Diphtheria, in like manner, is now known to be 

 caused by a microbe, bacillus cliphtheriticus. Erysipelas 

 too takes is rise from the working of a fungus. So also 

 does malarial fever, and the curious fact has been estab- 

 lished that it is projected into the human system by the 

 action of a female moscpuito, — 'taken from one person 

 and communicated to another. The processes of fermen- 

 tation and putrefaction, — and the familiar experience of 

 milk's turning sour in hot weather, — are all traceable to 

 the action of fungi, so minute that a microscope is needed 

 to discover them. Xor can you turn to a species of plant 



