36 HALF AN HOUR WITH SEAWEEDS. 



do they need any, as they do not draw their nutriment 

 from the earth, but from the sea water. The smaller 

 seaweeds have no appearance of roots at all, and, in 

 the larger, you will readily see that the fibrils of 

 the stem, which look like roots, are in reality only a 

 kind of clasper, to get firm hold of the rocks by. Their 

 usual mode of anchoring or attaching themselves is 

 by a sort of disk. This is seen more especially in 

 the chorda filum, or " sea-cord," an object you cannot 

 fail to have recognised in the dark olive, almost black, 

 round, cord-like weed, perhaps many feet in length, 

 which lay entwined among other seaweeds. This 

 particular weed often reaches the length of twenty 

 to forty feet. 



By far the commonest of these " black " spored 

 seaweeds is that group popularly known as " sea- 

 wracks," which you may see lying in dark, unattractive 

 heaps at low water. First, there is the " black tang," 

 or " bladder- wrack " (Fucus vesiculosus) y whose long 

 fronds are often two feet in length. These fork 

 repeatedly into what we may call branches, each 

 having a stout mid-rib running down the centre, and 

 covered with warty tubercles, or bladders, arranged 

 in pairs (Fig. 7). The presence of this mid-rib dis- 

 tinguishes the species vesiculosus from the nearly 

 allied species nodosus, in which the mid-rib is 

 altogether absent. The " bladders," to which we 

 have referred, are hollow, and filled with air, so as 

 to render the weed buoyant in the water. It is a 

 common practical joke with sea-side boatmen, to 



