The Causes of the Zoning of Brown Seaweeds. 55 
water. As soon as the tubes were removed from the water it ran 
out through the filter paper, leaving the young plants dry; the last 
few drops of water were expelled by blowing into the tops of the 
tubes. The plants were left dry, and in water, alternately for definite 
intervals of time ; thus imitating the periodic exposure by the tides. 
The results of four weeks’ treatment may be summarised as 
follows:— 
In water 11 hours, dry 1 hour, in every twelve. 
The plants of all four species were at about the same stage of 
development, most of them had a much divided rounded thallus 
with a well-developed branched pseudopodium, and a few hairs at 
the top of the thallus. In all the species certain specimens had 
reached only about the eighth division, and occasionally the thallus 
was perfectly round, without any development of a pseudopodium. 
In water 6 hours, dry 6 hours, in every tivelve. 
The specimens of Fuchs spiralis and Fucus vesiculosus were at 
nearly the same stage as in the former case; most of them having 
the much divided round thallus, occasionally with hairs, and 
attached by a well-developed pseudopodium. There were, however, 
specimens which had only divided about eight times and even only 
once or twice. The plants of Ascophyllum nodosum were at an 
earlier stage, the most advanced specimens showing seven divisions; 
while in the tube containing Fucus serratus no plant was found 
showing more than four divisions, and many had only divided twice. 
The pseudopodia were well developed in all these. 
In xvater 1 hour, dry 11 hours, in every twelve. 
The specimens of Fucus spiralis had many of them divided 
three times, though others showed only one division. The most 
advanced specimen of Fucus vesiculosus had three divisions, another 
had divided once, and several were not divided. The pseudopodia 
were well-marked in both these species. No germinated specimens 
were found in the tubes containing Fucus serratus and Ascophyllum 
nodosum, though several undivided oospores were found. 
It appears from these results that the species occupying the 
highest zones can germinate, and become attached under all 
conditions; but those growing in the lower zones will not germinate 
under the tidal conditions obtaining in the highest zones. It is 
noteworthy that Fucus vesiculosus behaves in this connection, as 
though it occupied a higher zone than Ascophyllum nodosum, which 
js the reverse of the order found on the shore in this locality. 
