THE PLANT WORLD. 191 



SPOT DISEASE OF THE VIOLET. 



The annual sales of violets throughout the United States is estimated 

 at not less than ^1,000,000. One of the most widespread and destruc- 

 tive maladies known to attack the violet is the spot disease. This dis- 

 ease has l)een discussed in the florists' journals under a variety of 

 names, but is commonly known as the "violet disease," growers not 

 generally recognizing the fact that there is more than one malady at- 

 tackinii; the violet. 



Owiny; to the ruva<2:es of this disease the cultivation of the violet 

 has been at>andoncd in n)any sections of tlie country, and in others it 

 has become necessary to adopt new methods of handling the plants 

 during the growing season. 



In view of the general interest in violet culture and the import- 

 ance of the knowledge of a means of })rcventing the disease, a bulletin 

 has been prepared l)y Mr. P. H. Dorsett, of the Division of Vegetaljle 

 Physiology and Pathology of the U. S. Department of Agriculture, and 

 will soon be issued as a Bulletin No. 23, of that Division, entitled 

 "Spot Disease of the Violet." 



The bulletin says the disease attacks the plants at any stage of 

 their growth, from the small unrooted cutting in the cutting bed to the 

 mature plant in full tiovver. Plants that make a vigorous, rapid, Init soft 

 or succulent growth, are most subject to the disease. Its tirst a})pcar- 

 ance is characterized by small, definite, usually circular, greenish or 

 yellowish white spots, resembling the bite or sting of an insect. They 

 vary in size from dots scarcely perceptible to the unai(.ed eye to spots a 

 thiity-second of an inch or more in diameter. The point of infection 

 is surrounded by a narrow ring of discolortd tissue, usually black or 

 very dark brown, l)ut it changes to a lighter shade as the spots grow 

 older. As the spot develops, the central portion remains unchanged 

 in appearance, while the tissues inmiediately surrounding it, either to 

 one side or more frequently in a circle, becomes diseased by the rami- 

 fying growth of the mycelium of the fungus through this portion of 

 the leaf. 



Various opinions have been expressed as to the cause of the disease, 

 and suggestions as to the possible cause of treatment are numerous. 

 Weakness of the plants, improper soil conditions, growing them in the 

 open fields where they are exposed to drought, rains, dews, and direct 

 rays of the summer sun, and lack of attention to proper heating, 

 ventilation, and fumigation of the houses, are among the explanations 

 advanced. 



So far as the writer is aware, there is at present no effective re- 

 medy for the disease when it has a foothold. The principal fungicides 

 in common use for the prevention and check of plant diseases have 

 frequently been tried for this trouble, but with varying results. 



