ORNAMENTAL PLANTS 479 



VIOLET 



Alteraariose, spot disease ^ (Alternaria Violce Galloway & 

 Dorsett). — This is one of the most mdespread and de- 

 structive of violet diseases. It attacks the plant at any 

 stage of its growth and upon any green part, but is most 

 destructive upon the foliage. It first appears as small, 

 definite, circular, greenish or yellowish-white spots, varying 

 from mere dots to 1 mm. in diameter. The light center is 

 surrounded b}^ a narrow ring, usually dark brown to black, 

 but turning lighter with age. As the spot enlarges the 

 freshly diseased tissue is usually watery and translucent, 

 and the center changes to yellow or gray- white and may 

 fall out. Frequently by the combined effects of several 

 spots the whole leaf is destroyed. If the air is damp, a 

 thin coating of rusty-colored spores may be seen in the old 

 spots. 



Damp, warm, cloudy, summer weather, unclean houses, 

 weak plants, poor stock, poor beds, are predisposing con- 

 ditions to disease. 



The Marie Louise is especially susceptible; the Lady 

 Hume Campbell much more resistant. 



To avoid the disease the houses should be kept scrupu- 

 lously clean, only strong stock used, infected material 

 picked and burned, and insects banished. Close attention 

 must also be given to ventilation, heating, shading, and 

 watering. The soil should be removed each season and 

 every means used to produce strong resistant plants. 



Cercosporose, leaf spot (Cercospora Violce Sacc). — 

 Large dead ashen gray definite spots are produced upon 



1 Dorsett. P. H., U.S. Dept. Agr. Div. Veg. Phys. & Path. 2.3, No- 

 vember, 1900. 



