428 DISEASES OF CULTIVATED PLANTS 



remains straight. The fungus also develops on the sheaths 

 of the leaves. Perithecia globose, crowded in the stroma in 

 which they are immersed; spores fusiform, hyaline, slightly 

 curved, 3-septate, with two or three simple or branched spines 

 at each end, 4-6x0-5-1 p. 



Although a true parasite, this fungus is comparatively rare 

 and cannot be considered as of any economic importance. 



ACTINONEMA (LIB.) 



Perithecia flattened, without a definite mouth, seated on 

 creeping fascicles of hyphae that radiate from a discoloured 

 patch of the host ; conidia i -septate. 



Rose leaf blotch (Actinonema rosae. Lib. =Asteroma 

 rosae, D. C.) is a very frequent parasite both on cultivated and 

 wild roses, forming purplish blotches on the upper surface of 

 the leaves ; fibrils radiate from the centre of the blotches, and 

 very minute black perithecia are attached to the fibres or 

 strands of mycelium. 



Perithecia very minute, without a definite mouth, and con- 

 taining very small i -septate conidia. 



When present in abundance, the leaves fall early in the 

 season, when usually a second lot of leaves and shoots 

 develop, which are killed by frost. Spray with potassium 

 permanganate, and be careful to collect and burn diseased 

 leaves. 



DIPLODINA (WEST.) 



Perithecia subcutaneous or erumpent, subglobose, papillate, 

 black, almost or quite glabrous ; conidia elliptic-oblong, 

 i -septate, hyaline. 



Spruce shoot disease ( Diplodina parasitica, Prill. = Septoria 

 parasitica, Hartig) has been shown by Hartig to be the cause 

 of considerable injury to the spruce, both in woods and in 

 the nursery. It has also occurred on Picea Menziesii, and 

 may probably attack other species. The presence of the 

 fungus is indicated by the leaves near the base of the young 

 shoots, or those in the middle, becoming brown and soon 

 dropping off. This usually happens in May. At first the 

 apex of the shoot remains unchanged in colour, but on lateral 

 branches it droops. Very frequently the disease begins 



