36 



THE SIMPLE HOLOCARPIC BIFLAGELLATE PHYCOMYCETES 



stead, McLarty found that for about a minute fol- 

 lowing the completion of cleavage the zoospores re- 

 mained faintly visible flanking the irregular vacu- 

 olar spaces (fig. 22). Then as the protoplasm be- 

 comes more homogeneously granular and somewhat 

 oleaginous in appearance again, the outlines of the 

 zoospores disappear, and the vacuoles regain their 

 even contours (fig. 23). This is the so-called homo- 

 geneous stage following cleavage which has been de- 

 scribed by most students of Olpidiopsis. Sporangia 

 in the stage illustrated in figure 23 may undergo a 

 prolonged rest period before liberating the zoo- 

 spores. That the zoospore initials do not become eon- 

 fluent during the homogeneous stage, as Butler (07) 

 believed, is shown by MeLarty's plasmolytic experi- 

 ments on sporangia in this stage. After a period of 

 about three quarters of an hour the zoospore seg- 

 ments become visible again (fig. 24), and shortly 

 thereafter the vacuolate areas disappear suddenly 

 and entirely. The zoospores soon assume their ma- 

 ture shape and begin to swarm in the sporangium, 

 and within a few minutes following this stage, the 

 tip of the exit tube opens. The zoospores then emerge 

 fully developed and swim directly away (fig. 25). 



Variations of the type of cleavage and zoospore 

 behavior described above for 0. Achlyae have often 

 been reported. In O. Saprolegniae and 0. Oedogo- 

 niorum, for example, Coker ('23) and Scherffel 

 ('25) noted that the whole content of the zoospo- 

 rangium may occasionally emerge to the outside as 

 a globular, naked, undifferentiated, protoplasmic 

 mass and then undergo cleavage into zoospores as in 

 Lagenidium and Pythitim. In 0. Pythii the zoo- 

 spores swarm for a brief period at the mouth of the 

 exit tube (fig. 1 14) and then come to rest in a cluster, 

 'according to Butler. After a few minutes motion is 

 resumed, and the zoospores, which are by this time 

 provided with two flagella, swim away. A similar be- 

 havior for the zoospores of 0. schenkiana was re- 

 ported by Scherffel (figs. 137, 138). This initial rest 

 period at the mouth of the exit tube and the subse- 

 quent ones which interrupt the active swimming 

 stage have been interpreted by Butler, Barrett, 

 Scherffel, and Diehl as evidence of primitive or rudi- 

 mentary diplanetism. In coming to rest the zoo- 

 spores may retract their flagella (fig. 4) and assume 

 spherical or elongate shapes (figs. 5, 6) but they do 

 not encyst. At least no empty vesicle is left behind as 

 they form new flagella and swim away. In O. 

 Oedogoniorum, on the other hand, Scherffel reported 

 true diplanetism. The primary swarmers are later- 

 ally biflagellate (fig. 153). The cystospores later 

 germinate, and an empty vesicle is left behind as the 

 secondary swarmer emerges. Whether or not the 

 position of the flagella on the secondary swarmers 

 differs from that of the primary swarmers is not 

 known. 



The accounts and descriptions in the literature on 

 the shape of the zoospores and relative lengths of the 

 flagella vary considerably. Most investigators have 

 described the zoospores as oval, elongate, and taper- 

 ing at the anterior end or somewhat reniform with- 



out a marked ventral furrow and with two flagella 

 of equal or almost equal length inserted in or near 

 the anterior end. Other workers have reported them 

 to be almost spherical, oval, pyriform and distinctly 

 heterocont (figs. 103, 158). Accurate data on the 

 exact location and relative lengths of the flagella are 

 lacking in most species. However, since the zoo- 

 spores swim fairly rapidly and undergo changes in 

 shape it is difficult to determine with certainty the 

 relative lengths of the flagella in living material. 

 Markedly heterocont zoospores have been reported 

 and figured for (). irregularis (Constantineanu, '01), 

 0. schenkiana (Scherffel, '25), and 0. Ricciae (du 

 Plessis, '33), while in the remaining species they 

 have been described as isocont or with flagella of 



plate 10 



O. Achlyae 



Figs. 39-53. Successive stages of nuclear division. Mc- 

 Larty, I.e. 



O. luxurious 



Fig. 54. Two young incipient zoosporangia and a larger 

 female thallus with an attached male thallus in a swollen 

 hyphal tip. Barrett, I.e. 



O. Achlyae 



(All drawings after McLarty, I.e.) 



Figs. 55-58. Successive stages in the development of a 

 parthenogenetic and a sexual spore. Incipient spores in 

 figure 55 surrounded by a hyaline, amorphous zone or 

 layer. 



Fig. 59. Incipient spore from fixed and stained material 

 showing centripetal development of spines at localized 

 points. 



Fig. 60. Remanent of border of amorphous zone form- 

 ing a membrane-like border around the tips of the spines. 



Figs. 61-67. Variations in the character of the exospore. 



O. vexans and other species 



Fig. 68. Young male and female thalli; nuclei dividing. 

 Barrett, I.e. 



Figs. 69-76. Stages in nuclear division from female 

 thallus. Barrett, I.e. 



Fig. 77. Gelatinization of intervening wall between the 

 male and female thalli prior to plasmogamy. Barrett, I.e. 



Fig. 78. Later state in gelatinization. Nuclei in small 

 male thallus dividing. Barrett, I.e. 



Fig. 79. Passage of male nuclei into female thallus. O. 

 luxurious. Barrett, I.e. 



Figs. 80-82. Nuclear pairing and karyogamy. O. vcxaus. 

 Barrett, I.e. 



Fig. 83. Mature resting spore with two attached male 

 thalli which still contain their protoplasm. O. Achlyae. 

 McLarty, I.e. 



Fig. 84. Resting spore with four attached empty male 

 cells. 



Fig. 85. One empty male thallus between two resting 

 spores. O. luxurious. Barrett, I.e. Drawn from photograph. 



Fig. 86. Small O. minor-like resting spore of O. various. 

 Shanor, '39a. 



Fig. 87. Early germination stage. Male thallus enveloped 

 by spiny exposure. O. variant. Shanor, I.e. 



