DISEASES OF CULTIVATED PLANTS 



dispersed by wind, and thus have become independent of 

 water as a means of spore dispersion. 



All the species are minute, some amongst parasitic forms 

 can only be seen when highly magnified, as Pythium de bary- 

 anum> causing 'damping off' in seedlings. In some genera 

 no trace of mycelium is present during any stage of develop- 

 ment, whereas in the white mildews (Peronospora, Phyto- 

 phthora, etc.) there is a copious development of mycelium 

 present in the tissues of the host, and also a forest of 

 conidiophores on the surface. 



A sexual mode of reproduction is more frequently present 

 in the Phycomycetes than in any other group of fungi. 



Massee, Geo., British Fungi, Phycomycetes and Ustila- 

 gineae. L. Reeve and Co., London. 



PROTOMYCES (UNGER) 



Parasitic in the subepidermal tissues of plants, generally 

 forming coloured, swollen patches, resting-spores numerous, 

 terminal or intercalary, produced on mycelium which soon 

 disappears, wall thick, usually consisting of two layers, 

 hyaline or coloured. 



The dense groups of resting-spores often form hard, 

 modular swellings on the host. Conidia are unknown. 

 On germination the thin endospore, crowded with minute 

 cylindrical, motionless spores, protrudes intact through a 

 rupture in the wall of the resting-spore. The liberated 

 spores conjugate in pairs, and afterwards produce a germ- 

 tube which enters the host-plant and develops into a new 

 parasite resembling the genus Synchytrium in habit, but 

 distinguished by the presence of mycelium. 



The species cannot be considered as destructive parasites. 



Protomyces macrosporus Unger, forms small, often 

 elongated warts on the stem and leaf-stalks of various kinds 

 of umbelliferous plants, more especially goutweed Aego- 

 podium podograria, resting-spores, subglobose or elliptical, 

 wall-smooth, yellowish-brown, 30-38 ju, diam. spores, cylin- 

 drical, colourless, 2-2*5 X I P- 



Protomyces rhizobius (Trail) forms small nodules on the 

 roots of Poa annua. 



Resting-spores in groups of from 2-8, mixed with 



