22 



THE SIMPLE HOLOCARPIC BIFLAGELLATE PHYCOMYCETES 



Parasitic in Gomphonema micropus in Hungary. 



Except for the oval shape of its thallus and zoo- 

 sporangia (figs. 22-25) this species does not appear 

 to have any particularly outstanding characters. 

 Scherffel believed that the primary zoospores (fig. 

 26) may encyst at once at the mouth of the exit tube 

 (fig. 27A) as in E. bacillariacearum and in Achlya 

 species or swim away as in Saprolegnia and encyst 

 later. Until more is known about this organism its 

 validity as a distinct species will remain doubtful. 



E. LICMOPHORAE Scherffel, I.e., p. 10, pi. 1, figs. 23-30. 



Zoosporangia solitary or up to 10 in a cell, spread- 

 ing open the diatom shell and becoming partially 

 extramatrical at maturity; oval, slightly elongate 

 with 1 to 10 exit tubes which are inflated, thick- 

 walled, and flask-shaped at the base and give the 

 mature sporangium and irregular, somewhat stellate 

 appearance. Zoospore diplanetic; primary swarm- 

 ers pyriform, 3 /x long, with two equal, apically in- 

 serted flagella which' are approximately twice as 

 long as the spore body; swarming within the spo- 

 rangium, emerging singly and encysting in a group 

 at the mouth of the exit tube; individual cysts 3.5 ft 

 in diameter; germination of cysts and structure of 

 secondary swarmers unknown. Resting spores sin- 

 gle, hyaline and spherical, 12/j., smooth and thick- 

 walled; with several irregular refractive globules, 

 lying in a spherical, 14 //, in diameter, cell or envel- 

 ope which may be connected by a short broad canal 

 or tube to an oval hyaline vesicle or companion cell ; 

 germination unknown. 



Parasitic in Licmophora sp. in Hungary. 

 As has been noted before, Scherffel regarded the 

 resting spore as a fertilized egg in a rudimentary 

 oogonium, and in this respect he believed that E. 

 Licmophorae may be closely related to Aphanomy- 

 copsis and Olpidiopsis. This species also shows con- 

 siderable resemblance to Eurychasma dicksonii and 

 E. perforans by its broad exit tubes and partially 

 extramatrical zoosporangia. Whether or not it is dis- 

 tinct from the latter species remains, however, to be 

 seen. 



EURYCHASMA 



Magnus, 1905. Hedwigia .41 : 347. 



(plate 6) 



Thallus intramatrical when young but becoming 

 partially extramatrical at maturity; oval, ellip- 

 soid, pyriform, dome-shaped, angular or irregular; 

 transformed completely into a zoosporangium ; wall 

 of mature thallus well defined and showing a marked 

 cellulose reaction when tested with chloro-iodide of 

 zinc. Zoosporangia solitary in a cell, hyaline, smooth, 

 oval ellipsoid, pyriform, angular or irregular with 

 1 to 3 broad exit papillae or short tubes which are 

 usually completely extramatrical. Zoospores either 



(1), coming to rest and encysting in the sporangium, 

 forming thus a network of polygonal cysts as in 

 Dictyuchus, later emerging from the cysts into the 

 central portion of the sporangium and then swim- 

 ming out; or (2), swimming out at once and pausing 

 for a few moments at the mouth of the exit papilla, 

 then gliding away without encysting. Zoospores 

 ellipsoid and pyriform, hyaline, containing several 

 small granules ; heterocont with the two flagella at- 

 tached near the anterior end. Resting spores un- 

 known. 



This genus includes at present two incompletely 

 known species which are parasitic in brown and red 

 algae. Our knowledge of the genus is based almost 

 entirely on E. dicksonii the life cycle of which is 

 illustrated in Plate 6. Until the last decade the zoo- 

 spores were described as posteriorly uniflagellate, 

 although in 1925 Scherffel predicted that further 

 study would show them to be biflagellate. Dan- 

 geard's and Sparrow's studies in 1934 confirmed 

 this prediction as is shown in figures 1 and 2. Ac- 

 cording to Sparrow, the zoospore comes to rest and 

 encysts on the host cell (fig. 3) and soon forms a 

 germ tube which penetrates the host cell wall. The 

 content of the zoospore passes into the host as a 

 naked body leaving the spore case and penetration 

 tube on the outside (fig. 4) as in Ectrogella, Py- 

 thiella, Olpidiopsis, etc. Within the host cell the 

 young parasite appears as a naked amoeboid proto- 

 plast (fig. 6) with one to several pseudopod-like ex- 

 tensions and resembles the early stages of Ectro- 

 gella Licmophorae. According to Lowenthal, it as- 

 sumes a position near the host nucleus (fig. 6), but 

 whether or not this migration takes place by inde- 

 pendent amoeboid movement has not been deter- 

 mined. Lowenthal believed that it remains naked and 

 surrounded by the host protoplasm until it is fairly 

 large and multinucleate (fig. 7). In the early de- 

 velopmental stages it is hardly to be distinguished 

 from the host protoplasm in living material, but as it 

 increases in size it becomes very vacuolate (figs. 8, 

 9), according to Sparrow. Petersen ('05) described 

 four distinct and successive maturation stages which 

 he believed are also characteristic of the Chytri- 

 diales as a whole. At that time, however, it was gen- 

 erally believed that Eurychasma belonged among 

 the chytrids. Since doubt has been expressed about 

 the sequence of these stages it is worthwhile to enu- 

 merate them at this point: 1, Stade protoplasmique 

 ordinare characterized by dense, almost avacuolate 

 protoplasm and division of the nuclei; 2, Stade glob- 

 uleux in which nuclear division and zoospore differ- 

 entiation have been completed, and the sporangium 

 is filled witli numerous closely appressed globules 

 of an oleaginous nature; 3, Stade ecumeux char- 

 acterized by an increase in size of the sporangium, 

 highly vacuolate protoplasm with the nuclei lying 

 in the peripheral region and the cytoplasmic bridges 

 separating the vacuoles, and by the disappearance 

 of the outlines of the zoospores; and 4, Stade a zoo- 

 spores regulierement disposes contre la membrane 

 in which the zoospores are regularly distributed 



