OI.l'iniOl'SIDAf EAE 



39 



tli.it they can be distinguished. All thalli therefore 

 appear to be potential soosporangia and male or fe 

 male thalli in the early developmental stages. This 

 is strongly suggestted by Mauriaio's figure 7 of 0. 



major which shows two male thalli attached to a 

 larger female thallus with an aborted exit tube. The 



male thalli art' indistinguishable from small young 

 ■OOSporangia also except lor their close association 

 with the female thalli (tig. 54). In fixed and stained 

 material, on the other hand, the female thalli can be 



recognised quite clearly by their staining reaction. 

 Barrett found that they have a marked affinity for 



Orange (i. while the zoosporangia and male thalli 

 readilv take up gentian violet. Mel. arty likewise 

 noted that the female thalli may he distinguished in 

 the young stages by numerous fatty bodies which 



stain brilliantly with crystal violet. 



Successive developmental stages of a parthenogen- 

 etic and a sexual resting spore are shown in figures 

 55 to 58. In hoth of the incipient spores are numerous 

 large refractive fatty globules, which later appear to 



decrease in size hut increase in number. The endo- 



spore is well developed in figures 56 and ■">(), hut in 

 figure 53 there is yet no evidence of the exospore. In- 

 stead, the incipient spores are surrounded by hyaline 

 or slightly amber-colored zones. The formation of the 

 exospore usually first Incomes evident as a homo- 

 geneous, amorphous layer which develops centri- 

 pctally around the spores and gradually replaces the 

 closely surrounding granular host protoplasm shown 

 in figure 54. It is in this layer or zone apparently 

 that the host protoplasm is transformed into spines, 

 warts, knobs, or a smooth undulating layer. In O. 

 Pi/tlui | figs. 118-120) Butler reported that the host 

 protoplasm condenses centripetally, so that at one 

 period the outer ends of the spines appear sharp and 

 fully formed while the proximal part is still envel- 

 oped in host protoplasm. The investing band of pro- 

 toplasm described by Butler is probably a zone in 

 which the host protoplasm is being transformed and 

 deposited as spines. A resting spore of 0. Achlyae 

 in the process of exospore formation from fixed and 

 stained material is shown in figure 59. The conden- 

 sation or deposition appears to be occurring along 

 radially oriented lines, and in certain regions the 

 lines an- localized and organized into conical groups 

 or bundles, which apparently represent incipient 

 spines. It is to be further noted that the lines do not 

 extend all the way iii. but are progressing from the 

 outer margin toward the center. That the layer or 

 zone shown in figure 55 is not merely a region filled 

 with cell sap may be demonstrated by microdissec- 

 tion. Mel. arty found by such studies that this zone 

 is a comparatively tough structural layer. After the 

 spines have been fully formed the boundary of this 

 layer may often persist as a thin membrane-like 

 structure ( rigs. ."Hi. 60) around the tips of the spines. 

 which gives the impression that the resting spore 

 Lies in an empty hyaline vesicle. Mel. arty found that 

 the exospore may be poorly developed in resting 

 spores which use up most of the host protoplasm in 

 the early developmental stages, and suggested that 



the extent of exospore formation, i.e.. length, thick- 

 ness, and abundance of spines, warls. knobs, etc.. is 

 dependent on the amount of host protoplasm present 

 at the time of its development. In that event, it will 

 obviously vary to a high degree and is not to be re- 

 garded as a stable diagnostic character. Further 

 more, the exospore composed of spines, warts, knobs, 

 or a s oth undulating layer does not give a positive- 

 cellulose reaction when tested with chloro iodide of 

 zinc. 



As noted above, the exospore may exhibit marked 

 variations in a single species. In 0. .lclili/ac it may 

 be smooth, even, or undulating in contour (figs. 56, 

 (il, 65, 66) as in 0. incrasxata ; composed of fine, 

 thread-like spines (fig. 61) as in 0. fihrillosa; broad 

 triangular spines, as in 0. minor (figs. 60, 63, 67) ; 

 long tapering curved spines (fig. 62) as in (). curvi- 

 spinosa; or partly smooth and spiny (fig. 65). Oc- 

 casionally, two resting spores and two male cells 

 may be enveloped by one exospore (fig. 66). Parthe- 

 nogenetic spores may vary in exospore structure to 

 the same degree as the sexual spores in O. Achlyae. 

 Similar but less extensive variations have been de- 

 scribed by Shanor ('39a) for 0. variant, and an 

 examination of figures 91 to 1 1 1 shows how variable 

 the earlier known species of Olpidiopsis also are. 

 The empty male thalli or companion cells likewise 

 may be smooth, echinulate, warty or spiny. Obvi- 

 ously, a character as variable as the exospore is of 

 little diagnostic value in distinguishing species. 



Returning to the description of plasmogamy and 

 karyogamy, it is to be noted that the male and female 

 thalli are multinucleate before they show any 

 marked visible differentiation as gametes, except for 

 relative size. Their nuclei may continue to divide 

 mitotically (figs. 68-76) up to and even during (fig. 

 78) the initial stages of plasmogamy as has been 

 shown by Barrett and McLarty. The first step in 

 plasmogamy in species in which it occurs through a 

 pore, according to Barrett, is a swelling and gela- 

 tinization of a portion of the intervening wall be- 

 tween the fusing thalli (fig. 77). In fixed and 

 stained material this region is usually heavily 

 stained. A more advanced stage of gelatinization is 

 shown in figure 78 where the cell wall material ap- 

 pears to be diffusing into the two thalli. The nuclei 

 in the male thallus are dividing while those in the 

 female are at rest, but it is not uncommon to find 

 them dividing in both gametes during plasmogamy. 

 After the so-called fertilization pore has been 

 formed the protoplasm of the male thallus begins to 

 How into the female (tigs. 57. 79). The passage may 

 be completed within a few minutes or last several 

 hours. Following plasmogamy, the fused protoplasts 



change in their susceptibility to stains and have a 



greater affinity for safranin. according to Barrett. 

 The gametic nuclei become irregularly distributed 

 in groups and decrease considerably in size. At the 

 same time the number of refractive oil globules in- 

 creases, and the fertilization pore closes. During 

 these processes the exospore undergoes differentia- 

 tion, as described above, and attains its definitive 



