18 SYNOPSIS OF BEITISH SEAWEEDS. 



than the frond, repeatedly forked, lerel-topp _ fruit 



in their apices ; receptacles Bpindle-shaped or bifid, a 

 / . Sp. PI. p. 162(3. (Atlas, PL III. Fig. 11.) 

 Focus distichus, / 



On rocks and Btones between tide-marks; seldom, < 

 in places where fresh-water Btr< the sea; often in 



land-locked hay-, and estuaries. Perennial Spring and 

 summer. 

 This species, in many respects, resembles F. r 

 with some varieties of which it has been occasional! 

 founded; but it has many characters by which it may at all 

 times be known, independently of the absence of vesicles, — 

 which character is too variable to be depended on, for in 

 many forms of F. vesiculosa* vesicles are wanting. F. ce- 

 ranoides may be readily known by its much thinner and 

 more transparent substance, and by containing a less quan- 

 tity of saline matters ; so that it dries much more rapidly 

 when removed from the water, and requires far less steep- 

 ing in fresh water when specimens are prepared for the 

 Herbarium. The usual habitat of this species is in places 

 where a good deal of fresh water mixes with the sea ; but it 

 is by no means confined to such places. In the Loch of 

 Stennis, Orkney, where the water is but faintly brackish, a 

 rery narrow variety is abundant. The greater the amount 

 of saltness in the water the broader is the frond, but in no 

 case is the substance so thick and leathery as in F. vesicu- 

 losus. 



12. serratus {The serrated Fucus); frond plane, dichotomous, 

 midribbed, serrated, without air-vessels ; receptacles flat, 

 terminating the branches, serrated, Linn. Sp. PL p. 1626. 

 (Atlas, PL III. Fig. 12.) 

 Hab. On rocky sea-shores, clothing the rocks at half-tide level. 

 Perennial. Winter and spring. Very common. 

 Fucus serratus abounds on all the Atlantic shores of 

 Europe, and occurs, though rarely, on the eastern shores of 

 America, but is not found, according to J. Agardh, in the 

 Mediterranean. It presents some varieties, chiefly distin- 

 guished by the greater or less breadth of the frond, and the 

 depth of the serratures. I have chosen one of the most 

 common states for illustration. In the variety inte t 

 mus of Turner the marginal serratures are very shallow 

 and sometimes obsolete, but always sufficiently marked to 

 prevent the species being mistaken. In his variety lati- 

 f alius, the upper branches are very much wider than the 



