14 Tansley and Fritsch. 
pools. A considerable number of unicellular blue-green species are 
found amongst the filaments of the larger forms. In a few cases 
green Algae ( Oedogonium , etc.) were found, occupying one or other 
of the pools, but the blue-green species are by far the most promi¬ 
nent and of these the Nostoc occurs in prodigious amount. It is a 
species (belonging to Section Humifusa, Thur. et Born, and possibly 
identical with N. Passerinianum Born, et Thur. var. halophilum 
Hansg.) with very short filaments, made up of small cells, each fila¬ 
ment being as a rule surrounded by a yellow sheath, whilst the 
whole colony is contained in a hard, greenish or yellowish invest¬ 
ment, which forms foliar expansions. It is not confined to the 
pools however, but also occurs in large quantity on the sand round 
about, almost to within the limit of high-tide mark. It lies loosely on 
the sand presenting a dry and withered appearance and is then of 
dark colour, so that at a first glance it is readily mistaken for the 
withered leaves of the Ipomcea, amongst the runners of which it is 
to be found in large quantity. It must serve as a rich manure for 
this latter plant and also for the coco-nut trees at the back of the 
Ipomcea-vegetation, where it occurs abundantly on the sandy soil. 
The same form was also met with on the sandy spit at Kalutara, 
where however none of the above-described fresh-water-pools were 
observed, and the same applies to its occurrence at Matara. 'This 
alga is so characteristic of the Ipomoea-vegetation at various points 
on the Ceylon coast, that our sketch of the latter would be 
incomplete without its mention ; it would be interesting to determine 
whether the same or a similar form is found on other tropical coasts. 
In Ceylon the same alga was followed up for some way inland on 
the sandy soil of the coco-nut plantations and it was also observed 
near the Bentotta river about two miles inland ; here also it occurred 
on a sandy substratum. 
2. The Barringtonia- Formation (Beach Jungle). It is difficult 
to find a well developed example of this formation on the coast of 
Ceylon, at any rate in the region of high rainfall, and this for a 
reason that has been already mentioned,—it has been all cut down 
to make room for coco-nut compounds. All that remains of the 
Beach Jungle on the typical flat sandy coast such as we have 
described, are a few of the smaller trees or bushes, which fringe the 
edge of the compounds or are dotted over the inner zone of the 
Pes-capme-fovmzLt'ion. Of these the three most conspicuous and 
widely distributed are Clerodendron inerme (Verbenaceze), Sccevola 
Konigii and Pandanus odoratissimus. These three are all ubiquitous 
