CHYTRIDIALES 73 



A single species, 0. radicia (De Wild.) Paschcr, is included 

 in the genus. It is parasitic on the roots of various plants, 

 especially the Cruciferac, and causes chlorosis. The genus 

 differs from Olpidium chiefly in the stellate aspect of the shrunken 

 resting spore. As originally described the sporangia dehisce 

 by a simple pore. Recently, however, Guyot (1927: 79) has 

 figured sporangia of 0. radicis provided with elongate exit tubes 

 and the question of the advisabihty of merging this genus in 

 Olpidium may well be raised. The wall of the resting spore in 

 Olpidiaster is colorless. 



The genus Chnjsophlyctis Schilbersky was included in the 

 Olpidiaceae by von Minden, and resembles Olpidiaster in having 

 a resting sporangium which is somewhat stellate in form, though 

 the wall differs in being dark colored. The genus is based on a 

 single species, Ch\ endobiotica Schilb., cause of the black wart 

 of potato. Further investigation has shown that this species 

 is in fact a Synchyfrium, and it is discussed under that genus in 

 the following family. 



3. Olpidium Schroter (1886: 180). 



The largest and best known genus of the family, containing 

 about twenty-five species on a variety of substrata, including 

 the tissue of higher plants, pollen grains, uredospores, mycelium 

 of Saprolegnia, various algae, and lower animals. Both swarm- 

 sporangia and resting spores are commonly developed. The 

 former are relatively thin-walled, globose to elhpsoidal, and 

 smooth. They germinate usually by a single prominent exit 

 tube, which penetrates the host tissue, ruptures at its apex, and 

 frees swarmspores. The resting spores are thicker-walled, 

 smooth or verrucose, and also germinate by swarmspores. The 

 following species are common. 



O. brnssicae (Wor.) Dang. — in cabbage (Fig. 11). 



O. pendulum Zopf — in pollen in water. 



O. endogemim (Braun) Schroter — in desmids. 



O. uredinis (Lag.) Fischer — in uredospores of rusts. 



O. zygnemicolum P. Magnus — in Zygnema. 



O. entophytum Braun — in Spirogyrn, Vaucheria, and Cladophora. 



O. oedogoniarum (Sorokin) De Wildeman — ^in Oedogonium. 



The genera Olpidium and Pseudolpidiopsis of this family and 

 Pseudolpidium and Olpidiopsis of the preceding family should 

 be discussed together since the similarity in form and aspect of 



