CHYTRIDIALES 83 



guttulate contents (Fig. 4 I, Q, Z', p. 72). This stout durable wall 

 undoubtedly serves during the rest period to protect the living contents 

 from the harmful, or lethal, effects of unfavorable factors in the en- 

 vironment. 



The thallus bearing the asexually formed spore is often indistin- 

 guishable at first from that which bears the zoosporangium. As it 

 matures, however, certain distinctive features become evident. For ex- 

 ample, the rhizoidal system of monocentric forms is frequently less 

 well developed than that of zoosporangial plants. The contents, partic- 

 ularly those of the reproductive rudiment, become highly oleaginous. 

 After the incipient resting spore has attained its maximum size and has 

 received the protoplasm of the rhizoids, its wall begins to thicken. 

 Coincidently, the many small globules coalesce, until at maturity a 

 single or, less often, several large ones are formed. The remainder of 

 the contents appears strongly condensed and sometimes may consist 

 of only a relatively thin peripheral layer around the centric or eccentric 

 globule. Since in the formation of the resting spore the contents do 

 not permanently contract, the mature structure usually completely 

 fills its container. 



The wall may be smooth or variously ornamented, colorless or pale 

 yellow to dark brown. In certain smooth-walled types, as for example 

 Rhizophydium fallax (Scherffel, 1925b), R. couchii (Couch, 1932), and 

 Chytridium olla (de Bary, 1884), it is clearly differentiated into an outer 

 and an inner layer. In these species the outer wall probably represents 

 the wall of the container; the inner, the wall laid down by the accu- 

 mulated contents of the rudiment. In C. lagenaria (Karling, 1936a), 

 R. ovatum (Couch, 1935a), and others the wall is described as consisting 

 of only one layer, and is evidently simply the centripetally thickened 

 wall of the container. Spines, blunt knobs, lobes, undulations, or rays 

 are the most common types of ornamentation. In rough-walled resting 

 spores two distinct layers may generally be discerned, an inner smooth 

 thin one and an outer thicker one which bears the characteristic or- 

 namentation. In the case of the roughened wall of Nowakowskiella 

 ramosa, however, J. Roberts (1948) indicates that the ornamentation aris- 

 es from an inner layer. In the imperfectly known Chytridium characii 

 (Scherffel, op. cit.) the outer wall is thick and warty, and clearly pris- 



