PYCNOCHYTRIUM. ll.S 



S. globosum, Schroet. Wliere the attack is severe, this causes 

 pearly swellings or incrustations ; it frequents plants like Viola, 

 Galium, Achillea, Sonchus, 3fi/sofis. 



S. mercurialis, Fuck., is very common on Mercurialu pcrcnnis 

 though st'ldoni injurious to it. One severe case is thus de- 

 scribed by Schroeter : " In spring the stem of the plant was 

 covered by a thick uneven glassy crust, which in course of time 

 became raised into wing-like processes running down the stem 

 and coated on both sides with white granules of the immature 

 parasite ; the leaves were completely rolled together, crumpled, 

 and covered with glistening prominences as with fine silver sand. 

 The plant in this condition developed poorly, scarcely flowered, 

 and soon died, so that by the end of September few diseased 

 examples could be found." 



CLADOCHYTRIACEAE. 



The vegetative body is frequently a l)ninehed mycelium. It 

 lives intercellular as a saprophyte, or intracellular as a parasite, 

 and forms intercalary or terminal swellings, in which zoospor- 

 angia or resting-spores are produced, then it disappears. Sexual 

 reproduction does not occur. The parasite lives in and forms 

 swellings on aquatic plants, or land plants in moist situations. 

 The genera Urophlyctis and Physoderma contain species parasitic 

 on higher plants ; together with the saprophytic Cladosiioranfjivm, 

 these are regarded by Fischer as sub-genera of Cladochytrivvi, 

 and as such they are also here regarded. 



Urophlyctis has both zoosporangia and resting-spores, Fkyso- 

 dcrma has only resting spores, CladosjMiranfjiinn only zoospor- 

 angia. 



Urophlyctis. 



The delicate mycelium is . unl)ranched, or only sliglitly 

 branched, and lives endophytic, boring through the walls of 

 the host-plant. At the place where a hypha enters a host- 

 plant it forms a swelling or collecting cell (sammelzell), which 

 generally becomes differentiated into a larger cell rich in contents, 

 and an outer smaller one with few contents, but with fine 

 terminal bristles. From the collecting cells new hyphae 

 originate and produce other collecting cells in neighbouring 

 host-cells. The zoosporangia are situated outside the host-cells, 



