APPENDIX I 305 



margin of the tidal zone where it is is only exposed at spring 

 tides. Also in deep pools higher up the shore. 



No. 5. Laminaria saccharina (" Oar- weed "). Distin- 

 guished from No. 4 by its simple frond with crisped edges. 

 Colour and habitat as in L. digitata. 



No. 6. Fucus ceranoides. Frond with mid-rib. Dis- 

 tinguished by the tapering shape of the receptacles, which 

 are either in pairs or forked. Air-vessels usually absent. 

 Colour : brownish-olive. Habitat : between tide-marks 

 wherever there is fresh- water influence. 



No. 7. Himanthalia lorea. The identification of this 

 species is rendered easy by the characteristic cup-shaped 

 region of attachment (the thallus proper), and long fertile 

 fronds. Colour : dark olive. Habitat : between tide- 

 marks in positions exposed to air. Very common on some 

 rocky shores, absent from others. 



No. 8. Ascophyllum nodosum {Fucus nodosus). Frond 

 linear, frequently enormously long (see Plate IX), without 

 mid-rib (or, one might equally well say, consisting entirely 

 of mid-rib). Air-vessels very large, occurring singly at 

 intervals along the middle of the frond. Receptacles ovate, 

 borne on short lateral stalks. Frequently bears tufts of the 

 epiphytic Polysiphonia fastigiata. Colour : olive-green. 

 Habitat : about half-way between tide-marks, particularly 

 on boulders. The common name is " Knotted- wrack." 



No. 9. Fucus seiratus (" Notched- wrack "). Frond with 

 broad mid-rib and strongly serrated margins. No air- 

 vessels. Reproductive organs, or conceptacles, distributed 

 over the whole of the distal portions of the fronds. Colour : 

 olive-green. Habitat : the lower part of the shore, immedi- 

 ately above the Laminarian Zone ; also in deep pools. 



Fig. 21. No. I. Cladophora rupestris. A conspicuous 

 dark-green alga occurring in thick, bushy tufts, in pools 

 from high to low tide mark. 



No. 2. Enteromorpha intestinalis . Frond unbranched, 

 inflated, arising from a very slender base and gradually 

 dilating to a rounded extremity. Colour : dark green. 

 Habitat : between tide-marks, either exposed near high- 

 water mark or in pools. Another common species is 

 E. compressa.. 



No. 3. Corallina officinalis. A common red seaweed 



X 



