378 DR. SARAH M. BAKER AND MISS M. H. BOHLING ON 
same physical factors as those of the marsh Fucoids—a confirmation of 
Borgesen’s contention that it is produced and reproduced vegetatively from 
one of the saxicolous Sargassums, 
The Fucaceæ may play an important part in the economy of a salt marsh. 
They may come in as pioneer vegetation after the ground has been raised, 
and to some extent stabilised by filamentous green alge. The true halo- 
phytes follow very closely upon the pioneer Fucus, and, after they have 
colonised the ground, the alge persist as an undergrowth, forming an 
efficient protection for seedling halophytes, as well as a ground mulch for 
the adult plants. In connexion with this undergrowth there may be a 
ground Нога, as well as a considerable epiphytic vegetation. One species, 
Fucus spiralis У. nana, is a characteristic colonist of the vertical or con- 
cave mud-banks caused by erosion, and may afford some check to further 
erosion. 
The zonal distribution of the Fucacei, at definite vertical levels, is main- 
tained upon the salt marsh ; the order of zoning remaining the same, for any 
two species, as that of a sheltered coast. But here the determining factor is 
not the time of immersion per tide, but the number of tides covering any 
particular level of the marsh. 
It is impossible to conclude a study of this kind without emphasising the 
need for more definite information about the physiology of the higher alge, 
The thallus of these plants is so plastic, that it responds to every change in 
environment with an almost machine-like regularity, and yet we are so 
ignorant of its physiological methods, that we cannot give reasons for even 
the simplest of our observations. How can one estimate the effect of exposure, 
without knowing whether the plant can carry on photosynthesis in humid 
air? What significance is there in determining the distribution of erypto- 
stomata without any knowledge of their function? There are, no doubt, 
great difficulties in the handling of the Fucaceæ in a physiological labora- 
tory; but we commend the matter to the attention of seaside physiologists. 
Finally, we must acknowledge our obligation to the many friends who 
have assisted us both in the field-work and in the more critical part of 
this investigation. Our thanks are especially due to Mr. A. D. Cotton, 
of the Herbarium, Royal Gardens, Kew, whose expert advice has been 
most valuable in unravelling our systematic problems; also to Miss Ellen 
Kucewiez, who construed for us the main portions of Arcichovskij's 
lengthy Russian paper on degeneration in Fucus, and to Professor Е. W. 
Oliver, under whose general direction the research has been carried out. 
The investigation was indebted to assistance given by the Perey Sladen 
Trust in so far as the work is based on observations at Blakeney Point. 
