INTRODUCTION. XIX 



reacliing at times the enormous length of forty 

 feet — but at this depth in general the large sea- 

 weeds are comparatively few, and the prevailing 

 plant is the curious coral-like Melobesia. The vege- 

 table forms now become more rare, and the plant- 

 like zoophytes assume their place when we enter 

 upon the Coralline zone, a district in which the 

 vegetable kingdom finds few representatives, but 

 many counterfeits among the zoophytic forms of 

 animal life. 



Before quitting the subject of the distribution 

 of the algae, it may be well to remind the reader 

 that wherever deep pools are left on the recess of 

 the tide, in them species not usually growing at 

 such a height will be found. A shore on which 

 rock-pools are numerous, about mid-way on the 

 beach, will generally be productive of a variety of 

 species which otherwise might only be procured on 

 the rocks laid bare during the lowest tides. 



Similarit}^ of colour in marine plants is a charac- 

 teristic feature that often accompanies plants of an 

 allied structure. Thus the olive-green series (Me- 



