34 
the upper limit of their distribution may be 30 yards 
higher up the shore than in September, corresponding to 
a rise of 8 feet in a vertical direction. 
Migrations such as have been described above also take 
place in pools if the volume and depth of the pool be 
sufficiently large. The following observations were made 
on the movements of Asperococcus fistulosus in a large 
pool on the shore at Port Erin. The pool in question lies 
rather high up on the shore but is about five feet deep 
at the seaward end where it is also protected by upstanding 
rock ridges from too great insolation. Landward it 
shallows markedly, its depth decreasing to a few inches. 
The sides are for the most part vertical and though the 
pool is distinctly above the zone of red seaweeds on the 
surrounding shore, many members of the Rhodophyceae 
find suitable habitats on its shaded sides. The total 
length of the pool is ten feet and its breadth five, offering 
an excellent opportunity for observation of periodic 
changes in the algal flora. Asperococcus fistulosus plants 
are to be found in January and February only in the 
well-lighted shallow end of the pool where they appear to 
take advantage of the best illuminated positions. The 
plants are small, slender and show only occasionally the 
irregularity of outline typical of normal plants. They are 
usually provided with plurilocular sporangia only and 
are now regarded as the winter form of A. /fistulosus, 
though at one time it was suspected that they might be 
a distinct species or at least a variety. The view now 
held is that they merely represent a seasonal growth 
form of the plant. In March these plants show no great 
increase in number and appear to be less flourishing 
than formerly though other and more robust plants— 
presumably the progeny of the first-comers—now make 
their appearance in a position about half-way between the 
shallow and the deep ends of the pool. These latter 
