256 BRITISH SEA-WEEDS. 



Genus CX. ULVA. 



Frond a flat, irregularly-shaped, leaf-like, green mem- 

 brane. Fructification, green spores, generally in groups of 

 four, scattered throughout the frond. — Ulva, from the Celtic 

 ul, water. 



This genus, as hitherto known to British botanists, 

 has been variously rearranged. As regards our native 

 species, it may be most conveniently divided into two 

 sections. One, which corresponds for the most part with 

 the genus Phycoseris of Kiitzing, has the frond com- 

 posed of a double layer of cellules, or rather of two 

 separable but closely cohering membranes. The other, 

 Ulva of Kiitzing, has only a single membrane or layer 

 of cellules. Believing it to be desirable to avoid as much 

 as possible all changes of names, I follow the example 

 of Dr. Harvey in his ' Nereis Boreali- Americana/ and 

 retain the name of Ulva for both sections. 



Ulva Linza. The narrow Ulva. 



Frond composed of two layers of cellules, from a few 

 iuches to more than a foot long, and from less than half an 

 inch to two inches wide, linear-lance-shaped, taper at the 

 base, more or less acute at the tip, waved at the margin, 

 of thin, membranaceous substance, and a bright grass-green 

 colour. Fructification dispersed over the whole frond. 



This species is annual, and grows during summer on 

 rocks and stones about midway between the tide-marks. 

 It is not very common, but may be found in many loca- 

 lities round our coast. The outline of the frond is 

 more regular than that of the fronds of any other 

 British Ulva, and the plant, particularly when seen grow- 

 ing under water, is very graceful and beautiful. Dried 



