DISEASES OF PLANTS. 131 



organ is diseased, it fails to perform properly the function required 

 of it. 



But, as you know, the eye may be too sensitive instead of dull. 

 It may shrink even from the faint light which struggles through a 

 darkened window. In this case the organ is performing more than 

 its proper work, and it is truly diseased. It is important therefore 

 to remember that any part of an animal or vegetable organism may 

 be either sluggish or too active in the discharge of the function 

 which the Creator has inrposed upon it, and either the torpidity or 

 the excessive activity constitute disease. If this is clear we are 

 prepared to consider certain conditions which constitute disease 

 in plants. Let us now apply our definition of disease to vegeta- 

 tion. Is a plant diseased when any part of its organism deviates 

 from its normal function ? Plainly the answer is yes, and 

 considered strictly as a scientific question, it is a correct answer. 

 But for the purposes of the present paper, the answer must be no. 

 A farm or garden plant is not necessarily called a diseased plant, 

 even when any of its parts deviate from their normal function, and 

 we must distinguish carefully between conditions which you term 

 disease in plants, and those which a botanist would recognize as 

 such. A few illustrations will make this plain. 



Take the wild rose, for example. This beautiful single flower is 

 made up of four circles of organs, two outer to envelop and 

 protect the two inner. The inside circles are the reproductive 

 organs of the plant, and by the proper discharge of their function, 

 the ovules are fertilized and become seeds, or embryo plants. In 

 order to ensure the perfection of the seed, the two inner whirls, 

 or circles, must be complete and active. Both the third circle 

 which is made up of yellow threads yielding a fertilizing dust, and 

 the fourth circle, containing the ovules, must be present and 

 sound. Now if you transplant the wild single rose from the 

 thicket in which it hides to your rich flower gardens, and place it 

 in the most fertile soil, you will observe that a change gradually 

 occurs in successive flowerings. For a year or two, you will see 

 that the four whirls remain as before, two envfiloping and protect- 

 ing, two to carry on the mysterious ofiBce of producing seed. After 

 a while it will be perceived that many of the yellow threads of the 

 third circle give place to the purple petals of the second circle, 

 and eventually they disappear, being merged into petals and 

 forming what we call a double rose. The double rose, in which 

 the yellow dust-threads have all been changed by cultivation into 



