Studies in the Autecology of Ascophyllum Nodosum Le Jol

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Abstract
A. nodosum at Aberystwyth, on Cardigan Bay, attains maximum development under somewhat sheltered conditions, forming in the middle of its wide zone a practically "closed community" of considerable stability and continuity. The width of the zone may, perhaps, be correlated with tidal behaviour, approximating to the middle 2-hourly period of flow of the neap tide. Plants in the middle of the zone attain greatest length, possess larger air-bladders and produce a greater crop of receptacles than those at the extremities of the zone. The ages of plants vary in different parts of the zone, those at the top averaging 4-5 yrs., in the middle 8 yrs. and at the bottom 6-7 yrs. One air-bladder is formed, normally, each yr. after the first sporeling year. Exceptional bladder formation is produced by injury. Greatest increment of apical growth occurs from May to July, very little growth is added from Nov. to May. General dehiscence of gametes takes place in Apr., the antheridia discharging slightly in advance of the oogonia. Dehiscence begins in receptacles at the apex of each plant and at the top of the zone proceeding to distal receptacles in about 2 days, and from top to bottom of the wide zone in about a week after initiation.

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