XVm INTRODUCTION. 



bare by the reflux of the tide, which is marked in 

 its upper part by the growth of Fucus canahcu- 

 latuS; Catanella opuntia, Enteromorpha compressa 

 and intestinahs, with other species that are not im- 

 patient either of exposure to the atmosphere, or 

 hurt by the streams of fresh water that take their 

 course over the beach at this height. Lower down, 

 the Fucus vesiculosus is the most frequent kind, 

 and is again replaced by the Fucus serratus and 

 nodosus. Below low-water the Fuci begin to disap- 

 pear, and the Laminarian zone commences. In 

 this we have species of the largest size known in 

 our seas, with long stems and large ribbon-like 

 fronds ] their stems are clothed with many beautiful 

 parasitical algse, and among them live myriads of 

 peculiar forms of animal life. In sandy places 

 the Laminarise are replaced by Zostera marina, 

 grass -wrack, the only example among our sub- 

 marine vegetation of the phenogamous or flowering 

 plants. The Laminarian zone extends to about 

 fifteen fathoms 5 at this depth, in quiet water, the 

 string-like Chorda extends its long slender fronds, 



