918 AQUATIC PHYCOMYCETES 



two plants usually lying parallel in the host. The segment of the thallus 

 which will become the oogonium swells, forming a spherical, ovoid, or 

 fusiform structure. The antheridia are unspecialized segments of the 

 thallus and each forms a tube which makes contact with the oogonium 

 and pierces its wall. The contents of the receptive segment then undergo 

 movement and contract, concentrating at the place of entrance of the 

 fertilization tube. This contraction continues during passage of anther- 

 idial material, after which the granular matter in the zygote collects at 

 first into two large refractive masses and then into one. A two-layered 

 smooth colorless wall is now laid down around the zygote. Zopf points 

 out that in L. rabenhorstii, in contrast to higher Phycomycetes, the 

 female gamete is still an amorphous mass at the time of fertilization 

 and does not round off until later. Lagenidium distylae Karling (1944g) 

 is essentially similar in the character of its sex organs to Zopf 's species 

 save that the thallus is monoecious and no fertilization tube is 

 formed. 



Some species have parthenogenetically formed resting spores. For 

 example, in Eagenidium parthenosporum Karling (1944g) the whole 

 contents of a thallus segment will contract and become surrounded by 

 a thick wall. In L. destruens Sparrow (1950), however, the contents of 

 the digitate thallus divide into as many as six segments, each of which 

 becomes a thick-walled resting spore. 



The resting spore in both Myzocytium and Lagenidium lies loosely 

 within the wall of the receptive cell, and closely resembles the oospore 

 of Pythium. The early stages of germination have been observed by 

 Dangeard (1903b) in M. vermicola. After resting a few months the 

 oospore becomes multinucleate and produces a tube through which 

 zoospores may possibly be discharged. 



Parasitism 



A few general remarks on the parasitism of this group are pertinent. 

 Specific information is inserted in the discussions of the various species. 



The Lagenidiales are primarily a group of parasitic fungi, although a 

 few, little-known, chiefly marine, forms are reported to be capable of 

 living saprophytically in nature. Lagenidium giganteum (Couch, 1935b), 



