6 J. H. PRICE, I. TITTLEY & W. D. RICHARDSON 



total numbers of plants examined and with Mediterranean proportions (see later); overwintering 

 of bases, with subsequent vegetative growth from them are, as indicated, very important. 



The decision on which period of the year is likely to yield most profitable field data on game- 

 tangia in southern British Padina is not easy. Ramon (\969a, b : 346) reported that P. gymnospom 

 in Mediterranean Israel often produces gametangia immediately below the site of injury ; this same 

 effect was noted when lesions were made in cultured material. Since P. pavonica quite commonly 

 disintegrates in situ in Britain, it may be that the time of maximum gametangial production should 

 be looked for during the period when plants are disintegrating, or in geographical areas where 

 thallus-wounding by detritus is maximal but not eradicatory, or both. The period of disintegration, 

 [September-] October-November [-December] in most areas, is later (or earlier!) than algal 

 collecting would usually be commenced. The effect in geographical areas where thalli are frequently 

 wounded could occur at any time, but a rhythm of predisposition to production of gametangia may 

 exist more or less in phase with the normal period of frond disintegration. There is little British 

 evidence for this effect of tissue disintegration one way or the other, although the few known 

 examples of gametangial (<$} material do derive from September collections (1892, 1894). Allender 

 (1977) made some interesting and relevant observations on Padina japonica in Oahu. Although he 

 did not indicate connection on a cause/effect basis, he made it clear that the gametophyte, growing 

 more quickly than the sporophyte under the influence of strong water movement and yet being 

 more flimsy and therefore more easily torn in those conditions, was nonetheless at the highest of 

 its very low percentage presence amongst the total population in winter (February; 7% of popu- 

 lation). These observations support the suggestion that disintegration or damage may accentuate 

 the production of gametangia by the gametophyte. Fagerberg & Dawes (1973), working with 

 Flordia plants of P. vickersiae from two sites and depths of 3 m and 1-2 m respectively, found 

 field gametophytes (all dioecious) only from November to March. No mention was made of 

 any connection with wounding or disintegration. 



Previous studies of gametangia of Padina pavonica have been virtually entirely on Mediterranean 

 plants (Reinke, 1877, 1878; Funk, 1955; Ramon & Friedmann, 1966; Ramon, 1969a, b, c). In this 

 major centre of P. pavonica distribution, the pattern of development in time and location seems to 

 differ from that towards range peripheries. The higher temperature regimes and levels of illumina- 

 tion, leading to generally more luxuriant and perennial populations, probably entail a more 

 continuous sequence of individual growth and degeneration, perhaps with gametangial formation, 

 than in the north. The recent treatment of reproductive phenology in Mediterranean P. pavonica 

 (Ramon & Friedmann, 1966; Ramon, 1969c) established that critical and extensive studies could 

 reveal much greater frequency of gametangia than previously suspected. Gametangial material 

 (principally monoecious [May and June] or dioecious [other months]) was detected at six locations 

 and, at one or other location, in all months of the year on the shores of Israel. At four locations 

 within the Bay of Naples (the classical locality for the P. pavonica gametophyte), large numbers of 

 collections were made in each of July (1964), September (1963), and October (1962), slightly biasing 

 results toward the period suggested as possibly important for gametangial detection on British 

 shores. Collections from Split, Yugoslavia (49 gametophytes, almost entirely dioecious, out of 71 

 plants), reported by Ramon (1969c), showed similar bias since made in October (1966). In shallow 

 depths (0-0-5 m) in the Bay of Naples, sexual thalli were comparatively rare and most of the game- 

 tophytes dioecious. This agrees well with vegetative observations and with the few old gametangial 

 records for Great Britain. With increasing depth, the percentage of gametophytic plants generally 

 increased and (1-1-5 m) varied from monoecious in July to predominantly dioecious in September 

 and October. At depths of 2-2-5 m, gametophytes (all monoecious) were present in July, September 

 and October, with the highest percentage (47-6 % of sample) in September. Samples were relatively 

 small and results may vary with larger numbers and sampling over more of the year. 



Evidence from British waters, as indicated, does not permit the assignment conclusively of a 

 significant role to wounding or frond disintegration in determining the apparently rare and late 

 occurrence of the gametophyte here. British waters warm up more slowly, even at shallow depths, 

 than the Mediterranean surface waters, and the equivalent (although lower) temperature conditions 

 to the Mediterranean summer situation may not be attained until well into the September- 

 October period, if ever, in southern England. Even in the Mediterranean (Capo Garofano, Bay of 



