INTRODUCTION. XV 



submerged America." The Sargassum bacciferum, 

 and another species, Sargassum vulgare, are occa 

 sionally drifted on our Atlantic coasts ; but neither 

 of them are natives of our seas, and therefore can- 

 not justly be included in the British Flora. The 

 Fucus Mackaii affords a British example of the 

 rootless algae ; it is found in several sea-water lochs 

 in the North of Scotland, where it vegetates quite 

 unattached, resting on the mud by its own weight. 

 The variety /S Balticus of Fucus vesiculosus also 

 vegetates in like manner in salt-water marshes occa- 

 sionally flooded by the tide. Several species of 

 Melobesia, stone-encrusted algse, are found lying on 

 the sandy bottom of quiet bays. The fresh-water 

 species of the genera Cladophora and Conferva, 

 mostly float in detached masses on the surface of 

 our ponds and ditches, while their marine associates 

 are often famished with small scutate roots. Entero- 

 morpha intestinahs is only attached when young, 

 afterwards it floats free on the surface of water — 

 growing indifferently in either salt, brackish, or 

 quite fresh water. 



