40 
DASYCLADEiE. 
really the growing point of the frond. I regard the disc as being properly a whorl of 
sporangia , united by their edges ; each radiating cell constituting a sporangium. The 
discs, after they have developed spores, are deciduous ; and new ones are successively 
formed, one above the other, as the stipe lengthens. 
1. Acetabularia crenulata, Lamour. -/margin of the peltate disc minutely crenu- 
late ; the cells apiculate (when young). Lam. Pol. Flex. v. 6, Tab. 8, Ha. 1. Kiitz 
Sp. Alg.p. 510. (Tab. XLII. A.) 
Hab. Rocks and corals, within tide marks, on the Florida reefs. Key West, W.H.H . , 
Prof. Tuomey (v. v.) 
Boot minute, discoid. Fronds scattered or tufted, two or three inches high, consisting 
of a slender, setaceous stipes, thinly coated with carbonate of lime, and bearing at its 
summit a peltate disc or cup, radiated like an agaric, and formed of clavato-cylindrical 
cells cohering by their edges, and filled with green endochrome. The stipes, when 
deprived of its lime by maceration in acid, forms a membranous, cylindrical tube, des- 
titute of markings, slightly enlarged upwards, having near its summit one, two, three, 
or more (according to age) annular swellings, from which issue whorls of very delicate, 
polychotomous, byssoid ramelli, and terminating in the first formed disc, from whose 
centre a pencil of similar byssoid fibres is produced. In further growth, the stipes 
proceeds through the first disc upwards for a distance of 1-2 lines, where another an- 
nulus emits a second whorl of filaments, above which a second disc is formed ; and thus, 
by successive apical growths new discs succeed each other, the older falling off as the 
younger are formed. In old specimens, therefore, you find the upper part of the stipe 
furnished with 4-5 or more annuli, marked with scars of the fallen ramelli and discs. 
In full grown specimens, the peltate disc, or circle of sporongia, is nearly half-an-inch 
in diameter. At first the matter contained in its cells is fluid and homogeneous. 
Eventually nuclei are formed in it, and the contents -of each cell is converted into 
numerous globose spores, the whole endochrome being consumed in the process. The 
cell-wall of the stipe is thick and concentrically striate. 
This species very closely resembles A. Mediterranean from which it is distinguished 
by the minutely crenulate margin of the disc. In A. Mediterranea the margin is 
quite entire. 
Plate XLII. A. Fig. 1. Acetabularia crenulata ; the natural size. Fig. 2. Apex 
of a young frond, before the development of the peltate disc. Fig. 3. A young disc, 
within which is a pencil of byssoid fibres. Fig. 4. A mature disc. Fig. 5. Apex of 
one of the radiant cells, from a young disc in which they are mucronate. Fig. 6. One 
of the radiant cells of a mature disc, converted into a sporangium , and full of spores. 
Fig. 7. Spores from the same : all the latter figures magnified. 
