This has already been described in abstract form (Naylor, 1954). The form of the zoospores and early stages in their germination are illustrated in Fig. 1 and in Plates 12 and 13. Correlation is seen between the lack of any phototactic responses of the zoospores and the random orientation of the germ tubes of the embryospores. Although there is no response to the direction of the incident light, a high light intensity is necessary before germmation will commence. Cutting down of light intensity was found to retard, or even prevent, germination.
Stages in the formation of filamentous germlings are illustrated in Plates 13A, 13C and Fig. 2A, and in the formation of discoid germlings in Figure 3 and Plates 12B, 12C and 13B. Usually disc formation results from lateral proliferation
[ unclear: ] 11—A [ unclear: ] growing on [ unclear: ] rocks at Portobello [ unclear: ] Biological [ unclear: ] 221053 showing the typical dusters of adult plants Photograph by Dr. E. J. Bath [ unclear: ] B. [ unclear: ] a belt just above the [ unclear: ] chondrophylla at [ unclear: ] Beach, [ unclear: ] Island 19254 The [ unclear: ] dumps [ unclear: ] again be seen
Plate 12—Photomierographs of living plants in seawater of three different cultures of [ unclear: ] 18 22 and 45 days old respectively Photographed 45 52 A 18-day-old plants from St Clam [ unclear: ] which branching of filaments and [ unclear: ] formation has begun B 22-day-old plants from [ unclear: ] Otago Many of the plants have well formed discs but a number of them have retained then filamentous form Hans can also be seen C 45-day-old plants from St Clan, showing well developed discs D, E—Photomierographs of terminal dividing cells of germlings of [ unclear: ] D 8-day old germling fixed at 01 30 hours and showing several [ unclear: ] and a late prophase [ unclear: ] Scale = × 2,750 E 13-day-old germling fixed at 03 30 hours and showing a prophase nucleus Scale = × 3,650
Plate 13—Photomerographs of fixed and stained plants showing [ unclear: ] A 5-day-old germlings with [ unclear: ] still visible it one end The majority of the cells contain only one of two plastids B 19-day-old discord germling, grown for 12 days in running seawater at Portobello Marine Brological Station C 20-day-old germling which has retained the filamentous form and showing branching and an increased number of [ unclear: ] per cell Two harts can be seen passing out of the [ unclear: ] plane to the left
from the terminal cells of a short filament. The discs increase in size to about 50μ and develop long, colourless hairs.
After about two months erect filaments arose from the prostrate systems both filamentous and discoid. At first these were uniseriate without a terminal hair, but soon became multiseriate with a single terminal hair (Fig. 4), as were the youngest plants from the shore described by Skottsberg (1907). Although these erect structures have not yet been grown to macroscopic dimensions, they are assumed to be the young stages of the macroscopic plants. Each germling gives rise to several erect filaments, which may account for the characteristic clumps in which the mature plants occur (Plate 11A).
After about three weeks, some of the filamentous germlings developed pluri-locular sporangia (Figs. 2B and C). The zoids were liberated in a single apical stream, but their fate was not followed. Plurilocular sporangia have not been seen on the discoid individuals. Filamentous growths scraped from mussel shells on which macroscopic plants were just beginning to reappear, and which showed similar details of cell structure to the germlings grown in culture, also bore plurilocular sporangia (Fig. 2D).