258 BRITISH SEA-WEEDS. 



which soon bursts into irregular segments, very thin and 

 delicate, of a pale yellowish-green colour, glossy, and adher- 

 ing closely to paper when dry. Fructification dispersed 

 throughout the frond. 



This species is distinguished from the preceding by 

 its fronds being composed of a single membrane, and 

 according to the arrangement to which I have alluded, 

 would be the only British representative of the genus 

 Ulva. It grows on rocks, shells, and small algge be- 

 tween the tide-marks in spring and in early summer, 

 and is annual. It is found in many localities round 

 our coasts, but is less common than either of the allied 

 species. 



Order XXIII. CONFERVACEiE. 



Frond green, thread-like, com/posed of cylindrical cells, ivhich 

 are usually of greater length than their diameter, and are 

 joined end to end. Fructification, minute, ciliated zoo- 

 spores formed from the colouring matter of the cells. 



A very large number of genera and species are in- 

 cluded in this order. Some of them are marine, and 

 others grow in brackish or in fresh water. It is very 

 difficult to describe them, or to determine with certainty 

 their generic and specific characters, and it is probable 

 that many which have been considered to be distinct 

 are in reality but different forms of the same plant. 



Genus CXI. LEPTOCYSTEA. 



Frond tufted, erect, jointed, branched ; cells elongate, 

 only one between each two sets of branches, filled with 

 granular endochrome, from which the zoospores are de- 



