THE BROWN SEAWEEDS OF THE SALT MARSH. 361 
cliffs lining the main channels, where it may be buffeted by waves and 
currents and where it hangs loosely over the concave banks and does not 
recline upon the mud. 
Although these conclusions may hold in a general way, they do not seem 
sufficient to account for the spirality of Fucus vesiculosus e. volubilis. The 
experimentally produced vegetative shoots of that species (figs. 12 & 13), 
although they show a good deal of curling and some spirality, had not nearly 
the spirality of corresponding shoots from the ecad volubilis produced in 
close proximity to the experimental plot. Johnson & York (1915) report 
from a similar experiment in Cold Spring Harbour (p. 62) that 6 ins. of 
spirally twisted thallus arose on the marsh in six months. It is probable that 
there is some hereditary tendency to spirality in the true marsh form, which 
is easy to understand, because the possession of a curled or twisted thallus, 
whereby it may secure an anchorage by entanglement with marsh vegetation, 
is a great asset to a limicolous Fucus. Intense spirality is an occasional 
character of attached Fucus vesiculosus, especially when the plants are 
spread out over mud; we have found certain plants as much spirally 
twisted as the marsh varieties. It is evident that the vegetative offspring 
of such parents have distinct advantages in the salt-marsh habitat, and also 
that any variations in the direction of increase in spirality caused by 
irregularities in the distribution of nutrient salts will tend to accumulate 
by selection. 
(c) VEGETATIVE REPRODUCTION. 
The substitution of vegetative methods of reproduction for normal repro- 
duction by means of oospheres and antherozoids, which was first recognised 
and described in detail by Sauvageau (1908, рр. 164-165) for Fucus vesi- 
culosus megecad limicola, is very general among marsh Fucoids. In trying 
to correlate this peculiarity with the new environmental conditions obtaining 
on the marsh, the question divides itself naturally into two parts. First, 
what factors cause the abortion of the sexual organs, and, secondly, what 
causes the great production of vegetative shoots, under marsh conditions ? 
A. Abortion of the Sexual Organs. 
In the first place it will simplify matters to eliminate some of the possible 
factors which might influence the produetion of sexual organs. The abortion 
of the reproduetive bodies is obviously not correlated either with exposure 
or the access of nutrient salts, or we should find, as in the case of the dwart 
habit, where these were the determining factors (see p. 358) that the Fuci 
from the uppermost zones were normal in this respect, whereas Pelvetia is 
the most consistently sterile of all the marsh Fucoids. Also it cannot be due 
to the absence of an attachment disc, as Svedelius (1901, p. 85) has suggested, 
for Ascophyllum nodosum ecad Mackaii, a free-growing form, fruits normally. 
