PLANT PATHOLOGY. 181 



in regard to the nature and origin of diseases is more likely to 

 avoid them than if lie were totally ignorant in regard to them. 

 And so it is with the diseases of fruit-bearing plants. It is not 

 likely that the grower will ever be able to dispense with the ad- 

 vice of the expert plant pathologist, but he will avoid a good 

 deal of trouble for himself and save much money (by saving his 

 fruit) if he knows some of the main facts and principles as to 

 plant diseases and their treatment. 



PLANTS ARE REALLY LIVING THINGS. 



What then are the things that the fruit grower ought to know? 

 First of all he should know fully that a plcmt is a living thing. I 

 know that in a certain way we all think of plants as living, but 

 very largely this is with some limitations and reservations. I re- 

 member the exclamation of a student in my laboratory, to whom 

 I showed some unusally active low form of plant, — "why it's 

 alive!' ' Yet I had talked and lectured to that student in regard 

 to the life of plants, and all that I had said had not penetrated 

 sufficiently to make him realize that life in the plant is like life in. 

 the animal. It was only when this life manifested itself in vis- 

 ible motion that its full meaning was understood. 



Plants are alive, and their life is the same as that of animals. 

 Not only is this true, but the life of a plant resides in the same 

 substance in both kinds of living things. If we examine the 

 animal substance under a compound microscope we find that it 

 consists of very minute bodies which are composed of proto- 

 plasm, — a soft and somewhat slimy substance. And so if we 

 make a similar examination of the plant substance we find simi- 

 lar minute bodies also composed of protoplasm. Now it is this 

 essential identity of structure, and the actual identity of life, 

 that I must insist upon here. The fruit-grower who is trying 

 to get an adequate notion of the pathology of his apple trees, for 

 example, must realize that they are as truly' alive as are his 

 horses and cattle, and that in their minute structure they are 

 essentially alike. 



SOME DIFFERENCES BETWEEN PLANTS AND ANIMALS. 



Now while apple trees and horses are essentially alike as liv- 



