CHLOROSPERMEJE, OR GREEN SEA-WEEDS. 89 



the margin of high-water, and increasing in luxuriance 

 with increasing depth, through the whole belt of ex- 

 posed rock ; but that the majority of them cease to 

 grow soon after they reach a depth which is never laid 

 bare to the influence of the atmosphere : and that the 

 Eed Sea-weeds (Rhodospermece) gradually increase in 

 numbers, and in purity of colour, as they recede from 

 high-water-mark, or grow in places where they enjoy a 

 perfect shade, or nearly total absence of light, and are 

 never exposed to the air, or subjected to a violent 

 change of temperature. 



The Green Sea-weeds are the simplest in structure, 

 and the least varied in species, on different coasts, and 

 consequently the least interesting to the collector of 

 specimens. With the exception of the beautiful genus 

 Cladophora, which contains about twenty species, our 

 British Chlorosperms are chiefly composed of Ulvce and 

 Enteromorphce, whose forms vary with so little order, 

 that it becomes difficult, and, in some instances, hope- 

 less, to attempt to classify the varieties. The Entero- 

 morphce are the first to make their appearance about 

 high-water-mark, covering loose boulders of smooth 

 rocks with a slippery vesture of bright green, or fill- 

 ing the shallow tide-pools with grassy fronds. These 

 plants consist of tubular membranes, simple or branch- 

 ed, appearing to the naked eye like fine green silk, 

 and showing to the microscope a surface composed of 

 minute cells, full of granules. The commonest species 

 near high-water-mark is E. compressa, which com- 

 mences of a very stunted size, and with thread-like 

 branches, if exposed to the air, and gradually acquires 



