30 



THE SIMPLE HOLOCARPIC BIFLAGELLATE PHYCOMYCETES 



this fungus. At maturity the protoplasm undergoes 

 cleavage in the filamentous thallus and exit tubes, 

 and forms elongate cylindrical segments (figs. 8-11) 

 which then pass out in succession in a linear row as 

 in Aphanomyces, according to Seherffel, round up, 

 and form a cluster of cystospores at the mouth of the 

 exit tube (figs. 7, 13, 14, 15). The lack of a differ- 

 entiated sporangium in Aphanomycopsis is one of 

 the chief characters which separates this genus from 

 Aphanomyces in Scherffel's opinion, but it may be 

 noted in this connection that Tokunaga found the 

 sporangia to be delimited by cross walls from the re- 

 mainder of the thallus. 



So far no evidence of sexuality has been observed 

 in Aphanomycopsis. Nevertheless, Seherffel re- 

 garded the thalli which bear one to several resting 

 spores as rudimentary oogonia, but the evidence for 

 this viewpoint is not convincing. In the process of 

 resting spore formation the protoplasm of the entire 

 thallus or segments thereof contracts into one or 

 more globular portions (fig. 20) which develop 

 thick, smooth hyaline walls and become dormant 

 (figs. 21-24). Whether these spores give rise di- 

 rectly to zoospores or a germ tube in germination is 

 not known. 



A. BACILLAR1ACEARUM Seherffel, I.e., p. 14. PI. 1, 

 figs. 31-35; pi. 2, figs. 36-18. 



Thallus 8-10 /x in diameter, continuous or septate, 

 not markedly constricted at septa; branches often 

 inflated at the end. Zoosporangia filamentous and 

 thread-like, or cylindrical, tubular, unbranched or 

 irregularly branched and lobed, 4.8-16.8 /x X 150 /x. 

 Exit tubes 4.8-7 /x X 150-240 /x, thickened and in- 

 flated at base to form a so-called "spreading appara- 

 tus" for separating the valves of the diatom cell. 

 Zoospore cysts at mouth of exit tubes spherical, 

 6-8 /x. Zoospores 7-8 /x X 10-12 /x. Entire thallus 

 functioning as a rudimentary oogonium (?) in con- 

 tinuous specimen; oogonia (?) intermingled with 

 sporangia in septate thalli, terminal or intercalary, 

 cylindrical and medianly expanded, 15.6-26.6 xi in 

 diameter, periplasm absent. Oospores (?) oval, 

 20 X 24 ii, spherical 14.4-20 /x, hyaline, smooth and 

 thick-walled with a large eccentric globule and a 

 bright lateral spot. For further details see generic 

 description above. 



Parasitic in Pinnularia I'iridis, Epithemia turgida, 

 Cymbella gastroides, and Nitsschia sigmoidea in 

 Hungary (Seherffel, I.e.) Pinnularia sp., and Syne- 

 dra sp., in New York and England (Sparrow, '33, 

 '36), Surirella sp., and Navicula sp., in Japan (To- 

 kunaga, '34). 



The parasite (fig. 7) which West and West de- 

 scribed in Pleurotaenium ehrenberghii is very simi- 

 lar and probably identical to A. bacillariacearum. 

 Their contention that this is the same fungus which 

 Archer ('60) described from the same host seems 

 very doubtful. 



bibliography: ectrogellaceae 



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