76 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



A CABBAGE DISEASE. 



By W. B. Grove, M.A. 



A LONG-KNOWN disease of various cultivated forms of Brassica — 

 Cabbage, Cauliflower, Broccoli, &c. — has been prevalent in the Isle 

 of Wight, Cornwall, and elsewhere during the past winter. Its 

 perfect stage is known as Mycosphaerella hrassicicola C. & De Not., 

 but it is somewhat rarely that the mature stage of the fungus is 

 found. More commonly it abounds and does considerable damage 

 in the imperfect or pycnidial stage, as indeed is the wont of many 

 of the parasitic fungi belonging to the Ascomycetes. 



The leaves begin to fade and are seen to be covered with numerous 

 crowded circular spots of a pale brownish colour, surrounded by a 

 green border and varying in size from about one-tenth to nearly 

 half an inch across. The surface of these spots is dotted over with 

 minute black points, arranged more or less in circular rings on the 

 brownish area. When these are fully developed, the spots look grey, 

 as if they had been sprinkled with a finely divided spray of ink. 



This imperfect stage was described many years ago as Aster oma 

 Brassicae Che v., but it is not an Aster oma in the modern sense, having 

 no " fibres " surrounding the pycnidia, as was recognized by Berkeley 

 when he first described it as British in 1841. Rather it should be 

 classed as a Phyllosticta, although in its early stages it seems at times 

 to come rather under the head of Gloeospormm, since the pycnidial 

 envelope is then very delicate and somewhat imperfect. As there is 

 already a Phyllosticta Brassicae Westd., having spores of a very different 

 character and a different arrangement of the pycnidia, the present 

 imperfect form will be named P. hrassicicola, with the following 

 description : 



Spots scattered all over the leaf, very numerous, more or less orbi- 

 cular, and marked with concentric circular lines, pallid, about 5-6 mm. 

 in diameter on the average, and at length fuscous in the middle 

 and surrounded by a greenish zone. Pycnidia very minute, delicate, 

 globose, sometimes imperfect, arranged (often concentrically) in the 

 centre of the spot, under the microscope translucent-olivaceous, 

 opening by a minute pore. Spores cylindrical, straight or occasionally 

 slightly curved, obtuse at the ends, frequently biguttulate, 4-5 X 

 i-ij^^. 



On the same spots, later, appear a large number of black perithecia 

 belonging to the Mycosphaerella. So far as we know, no culture- 

 experiments have been performed with this fungus, and the genetic 

 connexion of the two forms is a mere presumption, although a very 

 obvious and indubitable one. The perithecia of the Mycosphaerella 

 are of a loosely cellular dark-olivaceous texture, which is conspicuously 



