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77 



L. RABENHORSTI1 Zopf, 187a Verh. Bot. Ver. l'rov. 

 Brandenburg 90: T9. 1884 Nova Acta Ksl. Leop.- 

 Carol. IV.it. AJtad. Nat. 17: 145. PI. l. flgs. 1 -'*; pi. 

 .'. Bgs. 1-9. 



Th alias usually elongate, filamentous, tubular, 

 hypha-like when young, becoming septate, thicker, 

 . vesicular and more irregular, curved, and 

 crooked, with several short branches and protuber- 

 ances; Frequently attached to the host cell by the 

 infection tube and aoospore case; confined to single 

 cill or extending into adjacent host cells; usually 

 slightly constricted at the septa; segments elongate, 

 Id 20 p, cylindrical and often irregular, sometimes 

 breaking apart and separating; dwarf thalli usually 

 unicellular and often Olpidium-likt. Sporangia of 

 the same siae and shape as the thallus segments with 

 one straight, curved or tortuous, narrow, rarely con- 

 stricted exit tube, 2— 3 ju \ 5—20/1, which does not 

 project very far beyond the surface of the host; con- 

 tent of sporangium emerging and undergoing cleav- 

 age into zoospores outside of host; vesicle present. 

 or doubtful. Zoospores at first bean-shaped, later be- 

 coming more pyriform and reniforin, 6 X 8.5 /x, 

 isocont. Gametangia borne on the same or different 

 thalli: OOgonia terminal or intercalary, spindle- and 

 egg-shaped, locally paunchy and irregular, or al- 

 most spherical, up to 15 /t in diameter; antheridia 

 usuall v elongate and cylindrical. 5 X 15 /i, or some- 

 what irregular; sometimes borne on a delimited 

 branch from the oogonial cell, usually on an adja- 

 cent, or intercalary cell; developing a protuberance 

 toward the oogonium which elongates and tapers 

 into a perforation tube and pierces the oogonial 

 wall ; granules, bodies and discrete elements of the 

 ooplasm undergoing slight movement, and the whole 

 content contracting during plasmogamy; fused pro- 

 toplasts contracting further and becoming invested 

 with a wall. Oospores spherical 10— 15 /i, hyaline, 

 smooth, thick-walled with a large central refractive 

 globule; germinating within 24 hours by giving rise 

 directly to a large spherical 8 /i, biflagellate zoo- 

 spore ( : ). which soon infects the host cell. 



Parasitic primarily in the vegetative cells of 

 Spirogyra sp., Mougeotia sp.. and Mesocarpus sp. 

 in Germany (Zopf. I.e.. '79; Minden. '11 ); Spiro- 

 gyra sp. in Belgium (de Wildeman, '91. '93. '95) and 



Houmania Constantineanu. '01); OedogOnium sp. 

 in Denmark (Petersen, 09, ' 1 J ; Spirogyra sp. in 

 New York and Mass.. I". S. A. (Atkinson. '09; Spar- 

 row. '32 ) ; Oedogonium pluciosporum and S. ortho- 

 spira in Montana. U. S. A. (Graff, '28); Spirogyra 

 sp. and Mougeotia sp. in Bulgaria ( Valkanov, '31 ) ; 

 Spirogyra sp. S. mirabilis and Zygnema sp. in Hun- 

 gary (Cejp, '85; Domjan, '85). Spirogyra sp. in 

 England and Wales (Cook, '32. '33. '35). The writer 

 also has frequently found it in Spirogyra sp. and 

 Oedogonium sp. in New York City. 



Investigators are divided in their observations and 

 opinions about the presence of a vesicular membrane 



around the young zoospores in this species. Zopf and 

 Sparrow reported that zoospore cleavage and de- 

 velopment occur within a vesicle, like in Pythium, 



but Atkinson and Cook ('85) described the exuded 



protoplasmic mass as naked. In a previous paper 

 ('82), however. Cook had reported tin- appearance 

 of a thin membrane, while figure 9 and plate 1 of 

 his 1935 contribution arc very suggestive of its pres- 

 ence. Atkinson further described fusion of zoo 

 spores, but this appears to be an abnormal and pos 

 sibly pathological behavior and apparently has no 

 sexual significance. 



Cook ('35) maintained that the content of the 

 oogonium contracts and becomes invested with a 

 wall before fusion, forming thus a definite oosphere 

 or egg eel] which is attached to the oogonium wall by 

 a stalk. Zopf, on the other hand, who carefully 

 watched the successive stages of fusion at different 

 time intervals reported that contraction does not oc- 

 cur previous to but during plasmogamy and that a 

 wall or membrane is formed only after the process 

 has been completed. Cook's figure and description 

 of fusion are not particularly clear, and what he de- 

 scribed as an oosphere attached by a stalk seems to 

 be a fertilized oospore and a conjugation tube (tig. 

 15). 



Whether or not Cocconi's ('94) L. papillosum is 

 identical with this species is uncertain. Saccardo 

 ( '88 ) and Minden (11) regarded it as related, while 

 Cook believed it to be an incompletely described 

 specimen of L. rabenhorstii. According to his calcu- 

 lations of Cocconi's drawings, the thallus is about 

 5/i in diameter, the sporangia 17 /t, zoospores 4 X 

 6/i, oogonia 16 /i. and the oospores 10-12 /i in di- 

 ameter. The oospores, however, have a distinctly 

 warty wall, while the zoospores are figured as pyri- 

 form with two equal anterior flagella. Cocconi's 

 drawings of the zoospores, however, may possibly 

 be inaccurate. It is to be noted in connection that in 

 his early papers ('78, '79) Zopf also described the 

 oospores of L. rabenhorstii as being golden in color 

 and warty, but these observations possibly relate to 

 L. entophytum. 



L. ENTOPHYTUM (Pringsheim) Zopf, I.e., p. 154: 

 pi. .', 6gs. 10-18; pi. 3. figs. 1-3. 

 Pythium entophytum Pringsheim, 1858. Jahrb. Wiss. 

 Hot. 1: 2sr, 305. pi. J, tip. l. 



L. americaiium Atkinson, 1009. Hot. Gaz. 48: 334. Fig. 6. 



Thallus tubular, vesicular, short, relatively thick. 

 4-8 /i, curved, crooked and very irregular with nu- 

 merous short primary, secondary and tertiary 

 branches or protuberances; usually constricted 



slightly at the cross septa; dwarf thalli continuous. 



Sporangia of the same size. 5 >' 12 15 /<. and shape 



as the thallus segments and dwarf thalli. exit tubes 

 numerous, up to 20 or more, cylindrical and tortuous. 

 2 /i or more in diameter and of variable length. USU 

 ally inflated before passing through host wall, and 

 extending considerably beyond it; contents of Spo 

 rangia emerging and forming an irregularly glob- 

 ular mass at the mouth of the exit tube, which may 



sometimes float away before cleavage is completed; 



vesicular membrane doubtful or absent. Zoospores 

 bean-shaped and reniforin. 4 X 8 /i, isocont. Oogo- 



