VIOLET DISEASE. 



493 



The genus Alternaria is very closely related to Macrosporium ; the conidia 

 are almost identical, and could not be distinguished the one from the 

 other, save that in Alternaria they are developed in short chains, end to 

 end. I believe in some species of Macrosporium the conidia have passed 

 into a concatenate stage and been indistinguishable from Alternaria. Is 

 Macrosporium Violce really distinct from Alternaria Violce ? 



There is strong presumption in favour of the British being the same 

 as the American disease, but this cannot be verified until, by some means 

 or other, the conidia of the Alternaria can be found on the British Violets. 



It may be suggested, finally, as worthy of remembrance in connection 

 with these black moulds, that in some of the recorded investigations on 

 the life-history of Pleospora herharum it has been affirmed that Clado- 

 sporium passes into Macrosporium, and Macrosporiitm into Alternaria ; 

 so that the conidia of Cladosporium, Macrospiorium, and Alternaria are 

 all to be found together in the conidial stage of Pleospora herharum. 



VIOLET DISEASE. 



By Dr. W. G. Smith, Yorkshire College, Leeds. 



In September a parcel of Violets was received from the Hon. Secretary of 

 the Scientific Committee. As complaints have been common lately, it 

 was decided to grow the plants and observe them. On arrival there were 

 many dead leaves, but the roots were carefully packed and the plants 

 looked as if they would revive. They were planted in poorish soil from 

 a permanent pasture recently dug up in making the plots for the experi- 

 mental garden at the college farm at Garforth. At first the pots were 

 soaked with w^ater, covered with bell-jars, and kept in the laboratory. 

 Under these conditions many leaves died, but most of the plants rooted 

 and promised well. The dead leaves were then removed and the decaying 

 debris cleaned from the plants, the soil was allowed to become nearly dry, 

 and the bell-jars were removed for a few days occasionally. These 

 conditions produced a number of fresh healthy leaves, but the disease 

 never disappeared altogether, and could be obtained at any time by 

 covering a plant with a bell -jar for a few days. The course of the disease is 

 as follows : one or more yellowish-green patches appear on the leaf-blade, 

 generally near the margin ; these enlarge rapidly and the blade becomes 

 limp and withered, the leaf-stalk still remaining upright ; later the stalk 

 collapses. In some cases the leaf-stalk was first attacked : it soon collapsed 

 and the leaf fell to the ground. Various moulds were observed on dead 

 leaves ; we identified Botrytis and Mucor species. From time to time we 

 examined the spots on green leaves, and our observations agree with Dr. 

 Cooke's in his report. I could generally find a mycelium, even in early 

 stages of attack, but the Alternaria spores did not appear till later. On a 

 leaf almost completely killed I found spores which I took to be Cercospora. 

 There is a disease caused by a species of this genus 'on Violets. A 

 Phyllosticta has recently been reported on diseased Violets {Gard. Chron. 

 Nov. 1901), but I never observed any fungus suggestive of this. 



