Plate LXXIII. 



Fig. 342. ULVA LATISSIMA. 



Colour. A full, bright green; darker from deep water; fading pale; some- 

 times 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. 



Ilahitat. Our coasts generally. On rocks, &c. between tide-marks. Very 

 common. 



Called "green laver," in contradistinction to the 'purple laver {Porphyra 

 laciniata). Some authors call this species Phycoseris latissima; thus separating 

 it from the true TJlvas, which have the frond-membrane composed of only one 

 layer of little cells {cellules)', whereas that of TJlva latissima is composed of tioo. 

 Dr. Harvey, however, retains both under the genus TJlva, 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. ULYA LAGTUCA. 



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. 



Fructijication. As before. 



Habitat. Our coasts generally. On rocks, &c. between tide-marks. Not so 

 common as TJ. latissima. 



This is a true TJlva, the frond-membrane being composed of only one layer 

 of little cells [cellules). 



71 



