Plate LXXIII. 
Fig. 342. ULVA LATISSIMA. 
Colour, A full, bright green ; darker from deep water ; fading pale ; sometimes turning brown 
in drying. 
Substance. Membranaceous ; but quite crisp when fresh. 
Character of Frond. A ribless expansion of very irregular shape ; broad or oblong ; simple or 
divided ; wavy or flat ; often plaited ; one or more growing together from one base. 
Measurement. From 6 inches to 2 feet long ; from 3 to 12 inches wide. 
Fructification. Minute seeds {zoospores) formed of the colouring matter in the cells of which 
the frond-membrane is composed ; and in due time bursting through them. 
Habitat. Our coasts generally. On rocks, &c. between tide-marks. Very common. 
Called “green laver,” in contradistinction to \he purple laver {Porphyra laciniata). Some 
authors call this species Phycoseris latissima ; thus separating it from the true Ulvas, which 
have the frond-membrane composed of only one layer of little cells {cellules) ; whereas that of 
Ulva latissima is composed of two. Dr. Harvey, however, retains both under the genus Ulva, 
but points out the difference. This is only to be ascertained by dissection and examination 
under a microscope; but as a membrane with two cells is naturally thicker than those with 
but one, the firmer texture forms a distinguishing mark between this plant and the following. 
Fig. 343. ULVA LACTUCA. 
Colour. A pleasant light green, fading to yellowish ; sometimes darker when young. 
Substance. Delicately membranaceous ; almost transparent ; somewhat gelatinous ; thin. 
Character of Frond. When young, a puckered inflated bag ; afterwards bursting, and opening 
out into a flat, ribless, wavy or torn, more or less rounded expansion. 
Measurement. From 3 to 6 inches long, and as much wide. 
Fructification. As before. 
Habitat. Our coasts generally. On rocks, &c. between tide-marks. Not so common as 
U. latissima. 
This is a true Ulva^ the frond- membrane being composed of only one layer of little cells 
{cellules). , 
145 
