the Marine Algm of the Firth of Forth. 423 



destructive operation is to a large extent frustrated by 

 (1) the smooth external surface of the fronds, which pre- 

 sents the least possible resistance to bodies carried along 

 by the current, thereby reducing as far as possible the 

 strain exerted on its rhizoids, upon the maintenance of 

 which its own existence so largely depends ; and (2) by 

 its elasticity, which {e.g., in the case of Porphyrcc) is often 

 of so pronounced a character that its limit is not easily 

 exceeded, even by a directly applied apical strain. On 

 the other hand, at the period of maturation of the spores, 

 the benejBcial influence of foreign bodies carried along by 

 the water in facilitating the rupture of the spore mother- 

 cells or sporiferous conceptacles is self-obvious. This may 

 readily be observed in species of Enteromorphce, Monostromoe, 

 Porphyrcc, Fiici, Himanthalicc, Sphacelaria\ Ulothrices, 

 Bangia\ &c., and other similar external agents, as well as 

 the movements of Pectinidce., Crustacea (Hyas, Steno- 

 rhyjichv.s, Paguridce, and shore crabs), &c., cannot be over- 

 looked in the role which they play in bringing about, either 

 directly or indirectly, the emission of spores from the 

 protuberant urn-shaped ceramidia of the Polysphonice, the 

 globose semi-immersed and greatly protected coccidia of 

 the Plocamia, the round immersed favellidia of other 

 forms, or from the berry-like exposed favellse of Calli- 

 thamnia and Ceramia. 



But such agencies, though manifestly operative at the 

 periods of spore maturation, have had an earlier and no 

 less significant function to perform. Professor Dodel- 

 Port has already pointed to the importance of such 

 Infusoria as Vorticella in aiding in the cross fertilisation of 

 some Floridece, and from the large, delicate, and readily 

 destructible condition of the antheridia of Callithamnion 

 turneri, G. p)luniula, PUlota eleyans* Griffithsia corallina, 

 Geramium diaphanum, G. stridnm, and others, the direct 

 influence exerted by the impact of any foreign bodies, even 

 though inorganic, however small, in aiding the dissemination 

 of the antherozoids, and in facilitating their application to 

 their corresponding trichogynes, is readily demonstrable. 

 But these agents of cross fertilisation are, at the same time, 



* Compare T. H. Buffman's "paper in Jour. Quckct. Mier. Soc, ser, i. vol. i. 

 No. 8, pis. x,-xii., May 1884. 



