BCTROOELL Ml M 



28 



around the inner periphery of the sporangium. In 

 liirlit of what has since been discovered about zoo- 

 Bporogenesis in Pythiella, Ectrogella, and other 

 similar genera, it is very doubtful that numerous 

 large vacuoles arc present in the /oosporangium 

 after the loospores have been delimited, as Petersen 

 reported for stade ecumeux. Before cleavage begins 

 the vacuoles doubtless fuse to form one or more 

 larger central ones (fig. 12) which apparently disap- 

 pear when the centrifugal cleavage furrows reach 

 the plasma membrane, as Scherffel and Couch have 

 described for Ectrogella and Pythiella. It is. further- 

 more, questionable that nuclear division lias been 

 completed at the time of the stade globuleux. Peter- 

 son's studies relate only to living material, and in 

 SUch preparations it is impossible to determine when 



nuclear division is finished. Petersen's report that 

 these stages are characteristic of the Chytridiales as 

 a whole was denied by Scherffel who maintained 

 that they are typical only of the Saprolegniaceae 



and their elose relatives. Both he and Lowenthal re- 

 ported that the zoospores are delimited simultane- 

 ously, hut this is probably incorrect. Cleavage is 

 doubtless progressive as has been shown for other 

 closely related genera. 



According to Petersen, the zoospores become very 

 active within the sporangium, and after a while come 

 to rest and encyst around the inner periphery. They 

 thus form by mutual contact and pressure a periph- 

 eral layer of polygonal cysts — the so-called "net- 

 sporangium" stage (figs. 11. 11, 15). Sparrow, on 

 the other hand, observed that the zoospores usually 

 emerge at once and swim away ( Hg. 7) after a brief 

 pause at the mouth of the exit tube. He found the 

 "net-sporangium" stage only occasionally and con- 

 cluded therefore that its occurrence may possibly 

 be a reaction to adverse environmental conditions. 

 Nevertheless, two types of zoospore behavior have 

 been observed, one as in Saprolegnia and the other 

 as in Diet yuchus. It differs from that of the latter 

 genus, however, by the fact that the zoospores which 

 emerge from the cysts do not pass through the spo- 

 rangium wall but into the central cavity and then out 

 through the exit tubes. Whether or not those which 

 emerge directly and at once from the sporangium 

 encyst after a period of motility as in Saprolegnia 

 has not been determined. Petersen and Scherffel 

 nonetheless regarded the zoospores of Eurychasma 

 a^ diplanetic — the first motile stage occurring within 

 the sporangium and the second on the outside. So 

 far no one has figured or described the shape of the 



primary Bwanners within the sporangium, nor the 

 number, relative lengths, and position of their 

 flagella. 



The effect of Eurychasma on the host cell varies 



considerably as Rattray and subsequent workers 

 have pointed out. In some instances the infected 

 cells may not be greatly hypertrophied. while in 

 other cases they may be several times their normal 

 size. According to Sparrow, hypertrophy begins 

 shortly after the entry of the parasite ( tigs. .'i. 1. 5). 

 However, infected cells an- not stimulated by the 



parasite to divide; nor do the adjacent healthy cells 

 enlarge or divide as far as is now known. Hyper 



trophy is thus confined to infected cells. The en 

 Largement of the host cell does not keep pace with 



the growth of the parasite, since the latter eventu 

 ally bursts out of the confining host wall and is often 

 one-third to one-half cxtraniatrieal at maturity as is 

 shown in figures 10, 11. 11. IK, and 1!). According 

 to Lowenthal, destruction of the cell contents does 

 not occur at once in I'l/laiella cells, since the nucleus 

 and plastids may lu- clearly discerned even when the 



parasite almost completely fills the cell. The pyre- 

 noids. however, disappear very shortly. Sparrow, on 

 the other hand, reported that the plastids of Striaria 

 soon become discolored and disintegrate, and the de- 

 generated protoplasm which is not utilized by the 

 parasite eventually forms a brownish-green layer 

 around the mature parasite. 



Prior to the discovery that the zoospores of Eury- 

 chasma are biflagellate, this genus was generally in- 

 cluded in the family Olpidiaccae of the Chytridiales, 

 although as early as 1905 Petersen had made it the 

 type genus of a new family, F.urychasmaceae, which 

 he placed near the Olpidiaceae. Scherffel ('25), 

 however, merged Eurychasma with Ectrogella and 

 included it in the Saprolegniaceae, although it was 

 not then known that the zoospores are biflagellate. 

 He did this on the grounds that the thallus bursts 

 out of the host cell as in species of Ectrogella; that 

 the appearance of the protoplasm and the stages of 

 zoosporogenesis are similar in both genera, and on 

 the belief that the zoospores are typically diplanetic. 

 It is to be noted, however, that the "net-sporan- 

 gium" stage has not been found in species of Ectro- 

 gella. Furthermore, resting spores are unknown in 

 Eurychasma, and since it is not improbable that they 

 may be found to be quite different from those of 

 Ectrogella, Eurychasma is retained here as a sepa- 

 rate genus for the time being in the family Ectro- 

 gellaceae. 



E. DICKSONII (Wright) Magnus, I.e.. tips. 1-3. 



Rhizophidium dicksonii Wright, 1879. Trans. Roy. Irish 



Acad. 26:369. PI. 3. 

 Olpiditim dicksonii (Wright) var. Btriariae Wille, 1899. 



Vidensk, Selsk. Skr. Math. Nat Klasse 1. 3:3. PI. 3. 

 Ectrogella dicksonii (Wright) Scherffel, Ifl.'j. Arch. 



Protist'k, 52 :i, 11. 



Zoosporangia solitary, hyaline, smooth, oval, ellip- 

 soid, somewhat elongate. L'0-25 /j. X 10-80 /n, angu- 

 lar and slightly irregular with 1-3 short, broad, 

 cxtraniatrieal exit tubes or papillae. Zoospores oval, 

 pyriform 3 X 5 /», with two unequal flagella in- 

 serted near the anterior end. Resting spores mi 

 known. 



Parasitic in Edocarpus granulosus, E. CTinttuS, 

 Pylaiella littoralis and Striaria attenuata in Ire 

 land I Wright. I.e.; Johnson. '09); Ectocarpus con- 

 fervoides, E. crinitus and E. pusillus in Austria 

 (Hauck, '78): E. sUiculosus in Scotland (Rattray, 

 '81); Striaria attenuata var. fragilis and Pylaiella 

 littoralis in Norway (Wille, '99; Lowenthal. '05); 



