96 FUNGOID PESTS OF CULTIVATED PLANTS. 



the leaves, as the first indication of this disease. The spots gradually 

 spread, and the corresponding upper surface acquires a yellow colour. 

 It sometimes extends also to the fruit. On the leaves the spots soon 

 darken, and the leaves shrivel and dry. 



The mycelium consists of delicate colourless septate threads, which 

 penetrate the tissue in all directions, and sometimes overrun the entire 

 surface. From this mycelium arise erect fertile threads, which form 

 dense tufts, simple or shortly branched, pointed and flexuous, with the 

 joints swollen, and of a tawny colour. The conidia are produced at 

 the tips of the threads, mostly elliptical, with one division in the centre, 

 and pale brown (10-18 x 4-7 /u). Conidia may also be produced from 

 the nodules or short branches and are sometimes met with in short 

 chains of two to four attached end to end. They germinate readily in 

 water by sending out germ tubes, which become interlaced in a mycelium. 

 Spores placed on wounded fruit will produce rot. 



Two or three large cultivators have assured us that they have no 

 difficulty with this mould so long as they control temperature and 

 ventilation. Solution of sulphuret of potassium has been recommended 

 for spraying. 



Sacc. Syll. iv. 1731 ; Mass. PL Dis. 311, 435, fig. 83 ; Gard. Chron. 

 Oct. 29, 1887 ; U.S.A. Rep. 1888, p. 347, pi. iv. ; Journ. E.H.S. xxvi. 

 1902, p. 733, fig. 307 ; xxviii. pp. 142, 802. 



TOMATO BLACK ROT. 

 Macrosporium Tomato (Cooke), PI. VIII. fig. 121. 



This rot was also first observed in the United States before it 

 became known in this country. It makes its appearance at the apex, or 

 flower end of the fruit, when the latter is from half to two thirds grown. 

 At first a small blackish spot is seen, either around the remains of the 

 style, or on one side of it. This rapidly increases in size, but retains a 

 more or less circular outline. As the disease progresses the tissues 

 collapse quite regularly on all sides, and the berry becomes much 

 flattened. There is usually a slightly raised narrow border surrounding 

 the diseased parts x while just outside this the cuticle retains its normal 

 healthy colour, but appears slightly wrinkled owing to the collapsed con- 

 dition of the tissues beneath. Sections show that the black discolorations 

 extend deeply into the tissues. 



The principal cause of this disease is the black mould Macrosporium, 

 the mycelium of which consists of rather large septate, thick-walled, and 

 contorted threads, at first colourless, but eventually tinged with brown, 

 permeating all the diseased and decaying parts, and easily traced into 

 the sound tissue. Arising from the mycelium are the olive-brown fertile 

 threads, of variable length, which bear the large compound spores or 

 conidia. The latter are obclavate, attenuated above, and shortly stalked 

 below, divided transversely and longitudinally into as many as fifteen 

 almost cubical cells, after the manner of bricks in a wall, at first olive- 

 brown, becoming almost black (100-120 x 20-22 /*). 



All diseased fruit and the old stalks and leaves should be burnt. 

 Suggestions have been made for spraying with sulphuret of potassium. 



