MAN'S CONQUEST OF NATURE 579 



and foxes, destroy harmful rodents and may be considered of more 

 use than harm to the farmer. 



The Other Side of the Picture 



If we accept the statement that man is a rather doubtful conqueror 

 of his environment and the living things within it, we should look at 

 the other side of the picture and then attempt to strike a balance 

 between the forces which aid and which hinder man in his quest for 

 complete control over nature. Biological science must do more than 

 catalogue lists of economic victories over nature, or of battles won or 

 lost in the field of plant or animal husbandry. The facts noted in the 

 preceding pages ought to give the student a basis on which to build an 

 argument which will place man either on the defensive or in control of 

 the forces of nature that surround him. The bare facts related here 

 should be supplemented by much reading and investigation before a 

 conclusion is reached. When the facts are weighed, one sees that 

 man is by no means a complete conqueror, and that in some places 

 he even seems to be playing a losing game. By noting some of the 

 damage wrought by plant and animal enemies of man in the economic 

 world, and then adding the plants and animals that attack him, di- 

 rectly causing disease and death, we will be in a better position to 

 decide man's position as a potential conqueror. 



Harm Done by Plants 



In a general survey of harmful agents, bacteria and fungi stand out 

 as the most destructive. Leaving out death and illness due to bac- 

 teria which cause human disease, there is still a formidable list of 

 plant enemies which do much economic harm. Of the two billion 

 dollars of damage done yearly to the crops of this country probably a 

 third comes from bacteria and fungi. Bacterial infections cause such 

 diseases as wilts, which attack cucumbers and melons; fire blight, 

 due to a bacillus attacking fruit ; bean blight ; the black rot of cab- 

 bage ; and the soft rots that destroy many vegetables in storage. 

 The brown galls of fruit trees have been proven to be of bacterial 

 origin, as well as the watermark disease of the English willows, a blow 

 to the cricket players of England. Potato scab is caused by an 

 organism {Actinoryiijces scabies) closely related to bacteria. 



The algaelike fungi, or Phycomycctes, include water mold (*Sap- 

 rolegnia), the downy mildews, and the true molds. The plant disease 



