MACROSPORIUM 501 



Violet spot disease. This disease, caused by Alternaria 

 violae (Dorsett), is said to be one of the most widespread and 

 destructive maladies known to attack the violet in the United 

 States. Plants are attacked at any stage of growth, from the 

 small unrooted cutting to the mature plant in full flower. 

 Plants of rapid, succulent growth are most subject to the 

 disease. Any part may be attacked, but the injury is greatest 

 when the leaves are injured. Greenish or yellowish spots first 

 appear. As the disease extends, the spots present a waterlogged 

 appearance, and are semi-transparent ; afterwards, the affected 

 spot bleaches, and eventually falls away, leaving a hole in the 

 leaf. Unless checked, other spots appear until the entire 

 leaf is destroyed. Clusters of spores are formed on the spots, 

 and these quickly infect adjoining plants. 



Conidiophores erect, pale olive, septate, simple, 25X30X 

 4 fji ; conidia in chains at or near the apex of the conidio- 

 phores, clavately flask-shaped, muriform, strongly constricted 

 at the septa, olive, 40-60 x 10-17 /z. 



Bad cultivation, where much is expected without due 

 attention to cleanliness and the selection of healthy and 

 vigorous cuttings, is considered to favour the disease. 



Dorsett, (7.S. Dept. Agric., Pathology and Physiology Div., 

 Bull. No. 23 (1900). 



MACROSPORIUM (FRIES.) 



Usually forming blackish patches on living parts of plants, 

 Conidiophores clustered ; conidia dark coloured, muriformly 

 septate, often constricted at the transverse septa. 



Pycnidia and chlamydospores are present in some species. 



Potato leaf curl. Perhaps not one of the many diseases to 

 which the potato is subject is less clearly understood than 

 the present. This is because the general symptoms of the 

 disease, viz., yellowing and curling of the leaves, followed by 

 the collapse of the haulm, are by no means confined to the 

 disease under consideration, but are equally present as a 

 symptom of several other diseases, as in the case of Prillieux's 

 ' filosite,' where the leaves are small and curled, and the stem 

 long and slender. In this instance the cause is considered to 

 be of a physiological nature, owing to the constant reproduc- 

 tion of the potato by vegetative methods. 



