626 



THE GASES PRESENT IN THE FLOATS (VESICLES) 

 OF CERTAIN MARINE ALG^. 



By a. H. S. Lucas, M.A., B.Sc. 



Amongst our Australian Marine Algee, vesicles filled with gas. 

 are found only in a few genera of the Brown Seaweeds, Fucoidefe. 

 These are Sargassum, C nrpophyllum, Turbinaria, Cystophora, 

 Cysioseira (more typically a Northern genus), Scaheria, Phyllo- 

 spora amongst the Sargassaceaa ; Hormosira of the Fucacese; 

 Macrocystis, and possibly Adenocystis, of the Laminariacese. 

 Several receive their names from the habit. 



The function of the vesicles is evidently to support the fronds 

 in a more or less upright position in the water. In young plants, 

 alnd, in sheltered situations in shallow water, in even the mature 

 fruit-bearing individuals, there are no vesicles. This often causes 

 difficulty in the identification of a form which normally bears 

 characteristic vesicles. 



I have not seen anywhere any account of analyses of the gases 

 occurring in the floats of seaweeds, and have accordingly devoted 

 some little time to this inquiry as to the nature of the gaseous 

 content. Naturally the question of the origin of the gases is 

 most prominent in one's mind. There seem to be three possible 

 sources : (1) atmospheric air, (2) the gases dissolved in sea- water, 

 (3) gases produced in the metabolism of the plants themselves. 

 The main object of my experiments was to see if the results would 

 decide which of the three is the actual source. 



I may say, at once, that I have never detected any gases 

 beyond nitrogen and oxygen in the floats. It is hardly conceiv- 

 able that any process of metabolism should yield these two gases 

 only, without any carbon compounds. The issue is then narrowed 

 and the gases must We derived from those of the atmosphere, or 

 those dissolved in the sea-water. 



