94 TENTH ANNUAL REPORT OF 



up. This is a furtlier modification of the same idea, a further exten- 

 sion of the base of the cone. 



In all these cases the roots extend over flat surfaces, to which they 

 adhere by a series of discs. They show no tendency to penetrate 

 like the branching roots of perfect plants. The only instances of such 

 penetrating roots among the Alga? with which I am acquainted, occur 

 in certain genera of Siphonece and in the Caulerpece, tropical and sub- 

 tropical forms, of which there are numerous examples on the shores 

 of the Florida Keys. These plants grow either on sandy shores or 

 among coral, into which their widely extended fibrous roots often 

 penetrate for a considerable distance, branching in all directions, and 

 forming a compact cushion in the sand, reminding one strongly of the 

 much divided roots of sea-shore grasses that bind together the loose 

 sands of our dunes. But neither in these cases do the roots appear to 

 differ from the nature of holdfasts, and their ramification and exten- 

 sion through the sand is probably owing to the unstable nature of 

 such a soil. It is not in search of nourishment, but in search of 

 stability, that the fibres of their roots are put forth, like so many 

 tendrils. We shall have more to speak of these roots in the proper 

 j-)lace, and shall now proceed to notice some of the forms exhibited 

 by- 



THE FROND. 



T^he frond or vegetable body of the compound Alga3 puts on a great 

 variety of shapes in different families, as it gradually rises from 

 simpler to more complex structures. In the less organized it consists 

 of a string of cells arranged like the beads of a necklace ; and the 

 cells of which such strings are composed may be either globose or 

 cylindrical. In the former case we have a moniliforni string or fila- 

 ment, and in the latter a filiform or cylindrical one. The term filcmierd 

 (in Latin, ^'^wm) is commonly applied to such simple strings of cells, 

 but has occasionally a wider acceptation, signifying any very slender, 

 threadlike body, though formed of more than one series of cells. 

 This is a loose application of the term, and ought to be avoided. By 

 Kutzing the term trichoma is substituted for the older word filum or 

 filament. Where the filament (or trichoma) consists of a single series 

 of consecutive cells, it appears like a jointed thread ; each individual 

 cell constituting an articulation, and the walls between the cells form- 

 ing dissepiments or nodes, terms which are frequently employed in 

 describing plants of this structure. Where the filament is composed 

 of more series of cells than one, it may be either articulated or in- 

 articulate. In the former case, the cells or articulations of the 

 minor filaments which compose the common filament are all of equal 

 length ; their dissepiments are therefore all on a level, and divide the 

 compound body into a series of nodes and internodes, or dissepiments 

 and articulations. In the latter, the cells of the minor filaments are 

 of unequal length, so that no articulations are obvious in the com- 

 pound body. In Polysiphonia and lihodomela may be seen examples 

 of such articulate and inarticulate filaments. 



By Kutzing the terra johy coma is applied to such compound stems ; 



