L66 CEYLON PEAKL OYSTEE RETORT. 



(' Sitzungsber. d. Nied.-rhem. Gesellsch., Bonn, 14. Juni 1880,' p. 14G) maintains that 

 there are differences between H. tuna and //. platydisca, as regards the position of 

 the sporangia on the sporangiophores, but he does not give any figures. 



As to H. macroloba, the sporangia are mentioned by Zanarejixi (' Icon. Pliyc. 

 Adriat. et. Medit.,' vol. 3, p. 131) as having been seen by him, and they are stated 

 to lie similar to those of H. tuna. This remark on the fruits of II. macroloba, Decne, 

 is inserted by ZANARDINI in his description of Plate CXIL, which represents a 

 fruiting specimen of II tuna. Hence the reader might be led to imagine that the 

 fructification figured was that of //. macroloba and not that of H. tuna ; Zanardini, 

 however, merely emphasizes the point that he had not himself personally collected 

 the fruiting specimens of//, tuna which he figures, and that he had in his possession 

 fruiting plants of II. -macroloba, from the Red Sea, a district which was outside the 

 scope of his memoir. There is, therefore, no figure extant of the fruits of either 

 II. platydisca or //. macroloba. 



The fruits of H. gracilis grow out in small, short tufts from the margin of a joint 

 (see text-figures), but these tufts are confined to those jooints on the margin at which 

 the branches of the central strand emerge; and these branches, instead of continuing 

 their course so as to form a new side-joint, grow out into tufts of fruiting filaments 

 (figs. 1 and 2). In appearance, the fruiting joints of II. gracilis differ from those of 

 % H. tuna, which, according to the figures, bear a fringe of fruiting filaments along the 

 upper margin, and in some cases even in an isolated tuft from the flattened surface of 

 the joint. It is not quite easy to understand how this Aside, marginal fringe in 

 77. tuna can arise, since the strand of central filaments, from which the sporangiophores 

 spring directly, runs up through the centre of the plant and branches inside a joint 

 to form the side joints. If, as is always stated, the fruiting filaments of Halimcda 

 arise only from the filaments of the central strand and its branches, then the points 

 on the margin (or rarely surface) of a joint, where these strands emerge from the 

 tliallus. are clearly the only points at which fruiting filaments can be borne. 



An examination of the fruiting material of //. gracilis shows that the sporangia are 

 borne, as in II. tuna, on sporangiophores, which form a continuation of the filaments 

 of the branches of the central strand. According to the system of classification of 

 species followed in my paper referred to above, the distinguishing feature of 

 77. gracilis lies in the complete fusion of the filaments of the central strand in pairs 

 at the apex of a joint, the fused portion branching later trichotomously in the next 

 joint. When the fused portion is destined, however, to bear sporangiophores instead, 

 it branches dichotomously to form two sporangiophores, from which the sporangia 

 emerge all round and form a kind of loose raceme (fig. 3). In the material from the 

 Pearl banks of the Gulf of Manaar, most of the sporangia are empty, but it has been 

 possible to find specimens in which the protoplasm still fills the sporangia and the 

 apex of the sporangiophore. The protoplasm is studded with small, black dots, and 

 the condition is probably one shortly preceding the ejection of the zoospores. 



