612 



AQUATIC PH YCO M YCETES 



been observed, whereas in those species of Allomyces exhibiting sex- 

 uality, fusion of isogamous and anisogamous planogametes is the rule. 

 Isomorphic alternation of generations is found in all species mani- 

 festing anisogamous sexual reproduction. In those with isogamous 

 reproduction, the gametophyte may resemble the sporophyte {Blasto- 

 cladiella) or it may be represented by haploid zoospores which quickly 



Fig. 39. Diagram of life cycle of Blastocladiella variabilis Harder and Sorgel 



At the left are two gametophyte plants (gam.), each bearing a single game- 

 tangium from which are emerging isogamous planogametes. Gametes in one 

 gametangium bear an orange pigment, those in the other are colorless. 

 Gametes of opposite signs fuse in pairs to form a biflagellate zygote izyg.), 

 which germinates at once to produce the sporophyte plant. This may be either 

 a zoosporangial plant (zoosp.) or one bearing a single thick-walled golden- 

 brown resting spore (/•. sp.). Zoospores of zoosporangial plant reproduce new 

 sporophyte plants of either type; resting spore upon germination forms 

 planonts which give rise at germination either to or — gametophyte plants. 



(Modified from Harder and Sorgel, 1938) 



encyst and function as gametangia, forming four gametes each (Cate- 

 naria allomycis, Blastocladiella cystogena, Allomyces neo-moniliformis). 

 In Allomyces male and female gametangia are developed on the same 

 gametophyte thallus (Fig. 40 A-B, p. 616), whereas in "long-cycled" 

 genera which are monocentric, the gametophyte thallus bears either a 

 -f ora — gametangium (Fig. 39, p. 612). A further discussion of the 

 types of life cycles typical of Blastocladiella and Allomyces is given on 

 page 624. 



