22 AQUATIC PHYCOMYCETES 



to be due largely to a lack of knowledge of proper methods of collection. 

 It must be admitted, however, that some are, in fact, of very infrequent 



occurrence. 



In nature the aquatic Chytridiales utilize a variety of substrata, 

 namely, algae, other aquatic Phycomycetes, decaying plant debris, 

 microscopic animals and their eggs, and exuviae or empty integuments 

 of aquatic insects. 



Several methods are used in obtaining chytrid inhabitants of fresh- 

 water algae. The first of these is by the microscopic examination of 

 large amounts of material immediately after collection. This is a labori- 

 ous process, but it is necessary for those forms which are unusually 

 sensitive to environmental conditions and which are unable to with- 

 stand change. Another method is to place the material (small mats 

 of filamentous algae, scum of Euglena, and the like) immediately after 

 collection in shallow dishes of water in diffuse light, care being taken 

 to avoid overcrowding. Frequently, these conditions favor the devel- 

 opment of fungi, and in a few days a variety of chytrids often appears. 

 Still another and, perhaps, the most successful method is to set up a 

 gross culture of a fairly hardy alga, such as Cladophura, and place in 

 it bits of boiled algae, pollen, and herbaceous stems. After a few days 

 such "baits" frequently yield interesting fungi. The algae on which 

 chytrids are most often found are members of the Zygnematales (Con- 

 jugatae), Oedogoniales, and Cladophorales (particularly Cladophora). 

 Usually both living and dead plants of Nitella and Chara harbor a 

 chytrid flora. Chytridiaceous fungi are frequent on filamentous water 

 molds, such as Achlya and Saprolegnia, in old gross water cultures. 

 Bits of plant debris from aquatic, soil (terrestrial), or bog sites occasion- 

 ally yield chytrids upon direct microscopic investigation. A surer meth- 

 od, however, is to prepare gross water cultures with such debris or 

 soil cultures, 1 into which are put as bait small pieces of soft stem tissues, 

 such as corn or grass culms, bits of leaves of Elodea or Acorns, or root 

 tips. Care should always be taken to maintain a proper balance between 

 the amount of organic debris and the volume of water, so as to prevent 

 fouling of the culture. Most gross cultures of algae and debris support 



1 Soil cultures from cultivated land have a higher frequency of occurrence of 

 fungi and yield more varied forms than those from "natural" soils, see p. 17. 



