SECTION 17.] 



THALLOPHYTBS. 



167 



their decay. True as these general distinctions are, it is no less true that 

 these orders run together in their lowest forms ; and that Algse and Fun^ 

 may be traced down into forms so low and simple that no clear line can be 

 drawn between them ; and even into forms of which it is uncertain whether 

 they should be called plants or animals. It is as well to say that they are 

 not high enough in rank to be distinctively either the one or the other. On 

 the other hand there is a peculiar group of plants, which in simplicity of 

 composition resemble the simpler Algse, while in fructification and in the 

 arrangements of their simple cells into stem and branches they seem to be 

 of a higher order, viz. : — 



506. Characeae. These are aquatic herbs, of considerable size, abound- 

 ing in ponds. The simpler kinds (Nitella) have the stem formed of a 

 single row of tubular cells, and at the nodes, or junction of the cells, a 

 whorl of similar branches. Cliara (Fig. 550-552) is the same, except that 

 the cells which make up the stem and the principal branches are strength- 

 ened by a coating of many smaller tubular cells, applied to the surface 

 of the main or central cell. The fructifi- 

 cation consists of a globular sporocarp 

 of considerable size, which is spirally 



enwrapped by tubular cells twisted around it: by the side of this is a' 

 smaller and globular antheridium. The latter breaks up into eight shield- 



FlG. 553. Agarum Tumeri, Sea Colander (so called from the perforations with 

 which the frond, as it grows, becomes riddled); very much reduced in size. 



Fio. 554. Upper end of a Rockweed, Fucus vesioulosus, reduced half or more, 

 b, the fnictifioatjon. 



