132 BOARD OP AGRICULTURE. 



the purple petals, is incapable of reproducing its kind by seed. 

 The flower has thus been made to deviate from its normal function 

 of producing seed, and by our definition, the double rose is a 

 diseased flower. Nevertheless, the gardener seeks, by careful 

 selection and cultivation, to transform all the yellow stamens into 

 colored petals ; and by his art the richest of all flowers is produced. 

 You will see, at once, that there is a wide difi'erence between a 

 double rose, the type of health, and a flower attacked by what a 

 gardener terms a disease. It is plain -that the gai'dener has a 

 different conception of a disease from that which is conveyed by 

 our definition. 



There is a plant cultivated in gardens for its fine crimson 

 foliage, which well illustrates the difference. The plant, like the 

 common barberry, has green leaves which are to assimilate in the 

 air and sunlight, the crude juices brought from the roots through 

 the stem ; this power of assimilating the crude sap and working 

 it over into food for the plant, resides in the green tissue of the 

 leaves, and this power is diminished by a change in the color of 

 the leaves. When the barberry leaves become purple through 

 some causes imperfectly understood, it is my belief that the 

 assimilative power of the plant is lessened, and the plant is 

 diseased. But this diseased condition may be perpetuated by the 

 care of the gardener, and the purple color rendered a characteristic 

 feature of the plant. In the case of the purple barberry, and the 

 other plant, to which I have referred, the gardener has succeeded 

 in rendering permanent a disease of the leaf, because the diseased 

 plants are deemed more desirable for cultivation in gardens, than 

 the same species in perfect health. It is the design of the 

 gardener to render cettain plants diseased because they bring a 

 higher price. 



Therefore, we must for the purposes of this paper, modify the 

 definition of disease as applied to plants, and while we admit that 

 a diseased plant, is, scientifically speaking, one in which there is a 

 deviation from the normal function of any part, we must urge that, 

 in plant culture, a plant-disease is a condition in which there is 

 any such deviation from the normal function of any part as unfits 

 it for man's use. 



I sliall ask you to accept the following definition as one adapted 

 to the maladies of agricultural plants. A cultivated plant is 

 diseased when there is any departure from the normal function, so 

 that the value of the plant becomes impaired for the use of man. 



