810 AQUATIC PHYCOMYCETES 



fungus. Occasionally (Sparrow, 1934c; Aleem, 1953), however, the 

 diatom frustule was considerably distorted, so much so in fact as to 

 suggest that the fungus had dissolved the siliceous material and pro- 

 duced hypertrophy of the cell (Fig. 60 G, I, p. 806). One unopened 

 sporangium, presumably of this species, was found in which the mature 

 zoospores were loosely disposed around the periphery of a large central 

 vacuole, exactly as in Eurychasma (Fig. 60 I). No traces of a net spo- 

 rangium could be detected. This observation lends some support to the 

 contention of Scherffel (1925a) that Eurychasma should be merged with 

 Ectrogella. In the Danish material a resting spore was found to which 

 was attached a small hemispherical cyst, suggesting the occurrence here 

 of an Olpidiopsis-like, type of sexuality. 



Stages in the penetration of the fungus into the diatom were observed 

 in the American material. Many frustules bore quiescent zoospores on 

 the outer surface. In several diatoms a needle-like penetration tube from 

 the cystospore had pierced the cell wall. Actual passage of the fungous 

 material was not, however, observed, although empty epibiotic cysts 

 were found. Inside the cell the parasite assumed a central position, 

 possibly attaching itself to the nucleus of the alga. Once established 

 within the diatom it caused disarrangement of the chloroplasts and 

 eventually their total destruction. At maturity the sporangium was 

 surrounded by a few chestnut-brown residual granules, all that remained 

 of the host contents. 



Observations consistently showed that the fungus alone initiated the 

 infection and, unaided by other biological agencies, brought about the 

 complete disintegration of the diatom. During July infection of the 

 diatoms assumed epidemic proportions, as many as 88 per cent of a 

 population being invaded by the fungus. 



Ectrogella eunotiae Friedmann 



Osterr. Bot. Zeitschr., 99: 200, fig. 4, a-s. 1952 



Sporangium flattened ellipsoidal, assuming somewhat the shape of 

 the host cell, 1 1-21 \x broad by 17-52 [j. long by 5-7 y. high, wall thin, 

 smooth, colorless, discharge tube single, occasionally two opposite ones, 

 4-15 [j. long by 3.5-4.5 [x in diameter, with a broad, conical base, usually 



