EXPLOEATOBT NOTICES FOE JULY. 311 



Algce, from which the following extract may be inte- 

 resting. 



" In colour the Algae exhibit three principal varie- 

 ties, with, of course, numerous intermediate shades, 

 namely, grass-green, olivaceous, and red. The grass- 

 green is characteristic of those found in fresh water, 

 or in very shallow parts of the sea, along the shores, 

 and generally above half-tide level ; and is rarely seen 

 in those which grow at any great depth. But to this 

 rule there are exceptions sufficiently numerous to 

 forbid our assigning the prevalence of this colour 

 altogether to shallowness of water. Several of the 

 more perfect Confer vece and SipJwnece grow beyond 

 the reach of ordinary tides ; and others, as the beau- 

 tiful Anadyomene, are sometimes dredged from, very 

 considerable depths. The great mass, however, of the 

 green-coloured species are inconsiderably submerged. 

 The olivaceous-brown or olive-green is almost entirely 

 confined to marine species, and is, in the main, cha- 

 racteristic of those that grow at half-tide level, Algae 

 of this colour becoming less frequent towards low- 

 water mark ; but an olivaceous vegetation frequently 

 occurs also at greater depths, in which case it is very 

 dark, and passes into brown or almost black. The 

 red, also, is almost exclusively marine, and reaches its 

 maximum in deep water. "When red sea-weeds grow 

 above half-tide level, they assume either purple, or 

 orange, or yellow tints, and sometimes even a cast of 

 green, but in these cases their colour is sometimes 

 brightened by placing the specimens for a short time 

 in fresh water. The red is rarely very pure much 

 within the range of extreme low- water mark, higher 

 than which many of the more delicate species will not 



