%\t Bm-totfit Collector's #rak 



CHAPTER I. 



There is no country, I believe, that has so great a 

 variety of marine Algae as Great Britain. The shores 

 contiguous to Plymouth are peculiarly rich, both as 

 regards the number and rarity of species. 



In colour, the Algse exhibit three principal varieties, 

 with, of course, numerous intermediate shades, namely, 

 grass-green (Chlorospermese), olivaceous (Melanosper- 

 mese), and red (Rhodospermese). 



The grass-green colour is characteristic of those found 

 in fresh water, or in very shallow parts of the sea, along 

 the shores, generally above half-tide level, and is rarely 

 seen in those plants which grow at any great depth. 

 But to this rule there are exceptions, sufficiently nume- 

 rous to forbid our assigning the prevalence of this colour 

 altogether to shallowness of water. 



