FUNGOID PESTS OF CULTIVATED PLANTS. 53 



LOBELIA DOT. 

 Phoma devastatrix (B. and Br.), PI. III. fig. 62. 



For the first time, in 1856, the clumps of Lobelia in gardens were 

 attacked by a minute parasite, which was so destructive that it secured for 

 itself the specific name of " the destroyer." It is seldom that the fungi 

 of the group to which this pest belongs make any attack upon living plants, 

 being largely restricted to dead stems and dead leaves and twigs. 



The dots or receptacles, which, with their mycelium, represent the 

 entire fungus in this instance, are scarcely visible to the naked eye. They 

 consist of a minute globose body, like a pin-point, or a small black dot, 

 containing a number of colourless sporules, which are long and narrow 

 (8-10 fi), rounded at the end and furnished with two or three nuclei. 

 Fortunately in this case it took the form of an epidemic, which gradually 

 passed away, and for many years not an example has been seen. 



For a deep-seated disease like this there is no effectual remedy and no 

 protection, except to root up bodily all the plants which are, or are likely 

 to become, infected and burn them. 



This disease appeared afterwards also in the United States. 



Sacc. Syll iii. 791 ; Cooke Hdbk. No. 1221. 



About a dozen other parasites on Lobelia are recorded, most of them 

 in North America. 



PRIMROSE PARASITES. 



The Primrose family seems to be rather susceptible of fungoid diseases, 

 although perhaps their virulence is not upon an equality with their 

 number. The most dangerous, the rot-mould, has never established itself 

 as a pest, and the commonest are the leaf-spots. Most species of Primula 

 appear, however, to be liable to attacks from the rusts and smuts. 



PRIMULA LEAF- SPOT. 

 Phyllosticta primulcecola (Desm.), PI. IV. fig. 64. 



This endophyte is not a very common disease of the leaves of Primula 

 vera and Primula elatior in France and Belgium, whence it probably 

 extended to Britain. Discolorations sometimes seen on leaves of culti- 

 vated Primulas, which do not perfect themselves, may belong to this 

 species. 



The spots are white, circular, and rather large on both surfaces, with 

 a tawny margin. Sometimes the spots are naked, but at other times are 

 dotted with the minute blackish receptacles, which are then very 

 numerous, and, especially towards the centre, just visible to the naked eye. 



The sporules developed within the receptacles are exceedingly minute, 

 and are extruded in considerable numbers when mature (4-5 x 2-3 jj). 



Sacc. Syll. iil BOS', Cooke Hdbk. No. 1349; Grevillea, xiv. 74, No. 433. 



SCOTCH LEAF-SPOT. 

 Ascochyta Primula (Trail), PI. IV. fig. 65. 



This second leaf-spot has occurred in Scotland on Primula vulgaris, 

 and is exactly similar in external appearance to the foregoing. The 



