178 INTRODUCTION TO CEYPTOGAMIC BOTANY. 



are more simple in their structure than others, approaching, in 

 this respect, .Gonfervw. It abounds in species which display 

 the most exquisite combination of ramification and colouring. 

 The nuclei, which arise from transformed joints, are entirely 

 naked, or involucrate, simple, and filled with a mass of spores, 

 arranged according to no definite plan. Antheridia have 

 been observed in many species filled with active spermatozoids. 

 The threads are either strictly simple, or coated with filaments 

 or cells, frequently in transverse lines. The tetraspores are 

 often seated on the thickened parts in those species whose 

 frond makes an approach to inarticulate forms, but are some- 

 times contained in particular processes. In Ptilota and Micro- 

 cladia there is no external appearance of articulation, as in 

 CeraTnium. They are completely coated with cells, though 

 there is still an articulated axis. 



153. A large portion of our Nereis is composed of individuals 

 of this tribe, as they abound on our coasts in every little rocky 

 pool, on every piece of woodwork exposed to the waves, on 

 rocks and stones, and, above all, on the stems of the larger or 

 firmer Algae, or even on marine Phsenogams, which they fringe 

 in the most exquisite way with every shade of red, from a 

 bright rose to purple. They are represented by numerous 

 species in the southern hemisphere, and one or two Ptilotm 

 are amongst the most beautiful ornaments of subtropical seas, 

 nor, indeed, are our own seas destitute of the more highly 

 organised forms. There are, however, several genera which do 

 not affect more temperate regions. Microcladia glandulosa 

 is a rare inhabitant of our southern coasts, and differs from 

 Ceramium in its compressed fronds, besides other characters. 

 No genus is more natural than Ceramium itself. It comprises 

 many well-characterised species, several of which occur on our 

 coasts, and some of them are remarkable for their spinulose 

 branchlets. They are extremely elegant, from their trans- 

 verse alternate bands of white and red, and in almost all the 

 dichotomous branching and forcipate tips are very striking. 

 Besides these, however, there is a multitude of spurious species 

 which must eventually be weeded out of the system. The 

 species of North America are, for the most part, those of our 



