WITH NOTES ON OTIIKR SPECIES. 



89 



nuclei irregularly scattered through it. The protoplasm is at first pretty evenly dis- 

 tributed thi'ough the cavity of the oogonium, and encloses irregular vacuoles. Bat it 

 soon forms a definite parietal layer which is densest next the wall, and the vacuoles 

 fuse into a single large central one. The nuclei are still indefinitely arranged (Fig. 30). 

 They vary considerably in size, and in structure are identical with those of the vege- 

 tative filaments from which they are derived. After the growth of the oogonium has 

 ceased and the protoplasm has become parietal in position, the outer walls thicken 

 and the basal wall is formed, as already described. 



After an interval the parietal protoplasm begins to undergo changes preliminary 

 to becoming collected into one or more globular masses. We owe our first exact 

 knowledge of these phenomena to DeBary ('81), who studied them in several species. 

 The figures here given of the later stages of the process in a species not studied by 

 him, ^. apiculata, may serve at least to corroborate and supplement his account and 

 illustrations (Figs. 26, 27). The first change observed consists in the appearance in 

 the protoplasm of numerous light spots, approximately circular in surface view, which 

 may be seen to slowly shift their positions and eventually to disappear. These spots 

 were thought by Pringsheim ('58) to mai-k the positions of future pits in the wall, 

 which he regarded as perforations formed hj resorption. Reinke ('(>9), Cornu ('72), 

 and DeBary ('81), showed that the spots are much more numerous than the pits and 

 that they occur in all species without regard to the structure of the wall. It is 

 undoubtedly true that they are much more numerous than the pits in pitted oogonia 

 and that they bear no relation to them. DeBary's explanation ('81) of their nature 

 is supported by their appearance in section (Fig. 32). They are doubtless the expres- 

 sion of vacuoles in the parietal protoplasmic layer, formed by accumulations of cell- 

 sap, and finally empty into the central vacuole. Thus the central cavity becomes 

 gradually larger and the wall-layer correspondingly thinner and denser (Fig. 33), 

 The upper vacuole in Fig. 32 has united with the central one in Fig. 33. After the 

 vacuoles have disappeared, the proper degree of density having been reached, as we may 

 suppose, the protoplasm begins to flow towards certain regions and away from others, 

 causing a heaping up at the former and a thinning at the latter places. These accu- 

 mulations increase at the expense of the surrounding material until there are formed 

 a number of pretty distinct masses connected by a thin parietal sheet of protoplasm, 

 which is still a continuous lining of the wall (Fig. 2(3, a). This layer now breaks and 

 its rupture is followed by a large increase in the volume of the protoplasmic masses, 

 corresponding to the stage of swelling in the sporangium. At the same time, the 

 basal wall, previously convex downward, becomes reversed in position, indicating a 

 loss of turgcscence, as in the sporangium ; and the fragments of the parietal lining 



