Ser. CHLOROSPERMEA. Fam. Ul/vacee. 
Puate CCXLIII. 
ULVA LACTUCA, Linn. 
Gen. Cuar. Frond membranaceous, green, expanded, plane, (im some 
eases saccate when young,) composed of irregular cellules. /ructe- 
fication ; granules, often arranged in fours, scattered over the whole 
frond. Utva (L.),—supposed to be from Ul, wafer in Celtic. 
Utva Jdactuca ; “frond at first obovate, saccate, inflated, at length cleft 
down to the base; the segments plane, unequal, laciniated, semi- 
transparent.” —Girev. 
Utva lactuca, Linn. Sp. Pl. p. 1632. Lightf. Fl. Scot. p. 970. in part. Ag. 
Sp. Alg. vol.i. p. 409. Ag. Syst. p. 189. Lyngb. Hyd. Dan. p. 30. in part. 
Grev. Crypt. Scot. t. 313. Grev. Alg. Brit. p. 172. Hook. Br. H7. vol. ii. 
p- 311. Harv. Man. p. 170. 
Has. On rocks, stones, shells, and the smaller alge between tide-marks. 
Annual. May and June. Generally distributed round the British 
coasts, but less common than U. /atissima. 
Groer. Distr. Shores of Europe. 
Descr. Fronds tufted, from two to six inches high, at first forming an obovate 
bag, closed at the summit, but soon bursting, and split quite to the base 
into two or more segments which are often irregularly lobed or divided, 
the margin sometimes entire, but oftener jagged. Substance very thin and 
delicate, semi-transparent, closely adhering to paper in drying. Colour, a 
peculiarly beautiful light yellowish green. The surface glossy when dry. 
Under the microscope the frond is seen to consist of closely packed, quater- 
nate cells, lying in a transparent membrane. 
To Dr. Greville belongs the merit, as far as British naturalists 
are concerned, of having first clearly pointed out the characters 
by which this delicate plant may be distinguished:from the more 
common U. /atissima, and therefore I have thought it best to 
preserve the diagnosis given by that author in his Algee Britan- 
nice. ‘The eharacters are most obvious in an early stage of 
growth, when the present plant forms an obovate sac, not very 
unlike a greatly distended Hnateromorpha ; while U. latissima is 
at all periods of its growth a flat membrane. Other characters 
are found in the substance and colour. U. /actuca is of a brighter 
and yellower green, and more glossy when dry ; and its substance 
VOL. Hl. ‘¢ 
