52 SJEA MOSSES. 



the branches are divided and subdivided until they 

 are no thicker at the ends than human hairs. The 

 lesser branches are apt to be spiney. I have 

 specimens of JS. clathrata in my herbarium, whose 

 fronds ^re nowhere more than one-eighth of an inch 

 wide, though they are a foot and a half long. They 

 will be found of various lengths, from two or three 

 inches up. Under a high magnifying power, the 

 cells composing the firond will be found to be quite 

 square, and placed in a regular rectangular order, so 

 that the frond will appear tesselated or latticed; hence 

 its name. 



Genus.— &ZF^,* Z. 



The largest bright green plants in all seas belong 

 to this genus. Two species are usually quite large 

 when full grown, though there are plenty of them in 

 the young state, and the collector will find them in 

 abundance no more than two or three inches high. 

 The first two species are common on both coasts ; 

 the last grows only on the Pacific. 



Ulva latissima, L. 



The widest Ulva is extremely variable in size and 



♦ Ulva, from Ul = water in Celtic. 



