14 FOULING OF ships' BOTTOMS : 



(8) Notes on the Recognition of Specific Organisms. 



(a) Diatom Slimes. 



Among the types of diatoms responsible for fouling are species of 

 Schizonema, in which numerous individuals live within a branching 

 system of mucilage tubes (Fig. 40). The individual cells, according 

 to the position in which they he, appear rectangular or more usually 

 boat-shaped, tapering from the middle towards each end (Fig. 31). 

 Other diatom slimes are of a different character, the cells being 

 situated at the ends of rather thick, simple or branched, transparent 

 mucilage stalks, which are themselves attached to the ship's hull. 

 The commonest of these, due to a diatom called Achnanthes, is 

 readily recognised ( x 50), because the individual cells either appear 

 oval or exhibit a marked bend in the middle (Fig. 32), according to 

 the side which faces the observer. Less frequently diatoms are 

 found with wedge-shaped cells borne on mucilage stalks. These, 

 Ldcmophora (Fig. 30), usually grow attached to other seaweeds. 

 Many other kinds of diatoms occasionally occur in the growths on 

 fouled vessels, but these are rarely abundant and could only be 

 identified by an expert. 



(b) Plants. 



Among the greeM seaweeds the commonest is Enteromorpha 

 (Figs. 2 and 38), which possesses soft and rather flexible threads, 

 frequently unbranched, although a few kinds branch freely. Under 

 the microscope ( x 50) the threads can be seen to resemble a hollow 

 green tube, a layer of small cells surrounding the central hollow. 

 The cells are commonly arranged in longitudinal rows (Fig. 36). In 

 some of the coarser kinds the tube-like character is recognisable 

 without microscopic examination. The strand of Enteromorpha 

 may grow to a length of 6 in. or more. 



Less commonly the green seaweed Cladophora (Figs. 4 and 39) is 

 concerned in fouling. This occurs in dense tufts, which are richly 

 branched and usually from 1 to 2 in. long. They have a coarser 

 '• feel " than the gro\\i:hs of Enteromorpha, and with a good hand- 

 lens can be seen to consist of simple rows of long cells (Fig. 33), much 

 larger than those forming the surface of the Enteromorpha tube. 

 The branches commonlv arise in twos or threes at the same point 

 (Fig. 33). 



Occasionally green fouling is due to Urospora; this has un- 

 branched hair-like threads, which, when handled, have a rather 

 slimy feeling. Structurally ( x 100) they show a single row of broad, 

 often barrel-shaped, ceils witli rather thick walls and dark green 

 contents (Fig. 37). The shape and size of the cells are very variable. 



In the early stages of fouling very much narrower threads with 

 small cells are sometimes found ; they belong to the seaweed Ulo- 

 thrix flacca (Fig. 29), and are recognisable only under a microscope 

 ( X 100). Such threads sometimes occur within the diatom slimes. 



