116 AQUATIC PH YCO M YCETES 



An interesting feature of Micromyces, and one repeatedly noted, is 

 the strong attraction of the young thallus for the host nucleus. Couch 

 (1931) has intimated the value of this tendency to the fungus, which, 

 by thus achieving a central position in the host cell, is enabled to 

 make contact with the cytoplasmic strands of the alga. Since these 

 are attached to the pyrenoids, the fungus is in an advantageous po- 

 sition for utilizing the reserve food. The young thallus apparently 

 reaches the nucleus either by its own slight amoeboid motion or by 

 cytoplasmic currents of the host. Possibly a tactic response to nucleic 

 acids aids it in making contact with the nucleus. In Spirogyra cells 

 attacked by Micromyces contraction, disintegration, and discoloration 

 of the chloroplasts gradually take place, and eventually the entire 

 contents are reduced to a granular, often brownish mass within which 

 is imbedded the reproductive structure (prosorus or resting spore) of 

 the chytrid. 



In diatoms infected with such epibiotic forms as Chytridium perni- 

 ciosum and Rhizophydium fusus the changes brought about by the in- 

 vading rhizoids are well marked. Soon after infection thechromatophores 

 lose their golden-brown color and tend to become yellow green to 

 green. The cytoplasmic membrane contracts somewhat, and the yellow- 

 green chloroplasts become dislocated and eventually fragment. At 

 maturity of the fungus there frequently remain in the frustule only a 

 few chestnut-brown refractive granules. 



Perhaps the most unusual and vivid color changes produced by a 

 chytrid are those resulting from infection of Filarszkya, a blue-green 

 alga, by Rhizosiphon crassum (Scherffel, 1926a). No appreciable change 

 is noted in the infected host cell until the thallus of the fungus is 5-6 \j. 

 in diameter. The infected cell as well as adjacent ones then turns deep 

 wine-red, as if the chytrid were producing a poisonous substance which 

 was diffusing through the filament and causing the death of the cells. 

 As the fungous thallus enlarges and the broad absorbing organ in- 

 vades more and more of the filament, the cross walls are broken down, 

 and new cells become discolored and filled with a clear red-violet or 

 bluish liquid. By this time, the cells first infected, whose contents 

 have by now been partly or almost wholly exhausted, have turned 

 bright orange and contain light orange-brown granules of unassimi- 



