534 



INTRODUCTION TO PLANT GEOGRAPHY [CHAP. 



inland saline waters ranging from saturated brine to slightly brackish 

 lagoons, etc., was mentioned in Chapter XV. 



The Pacific Ocean supports a widely different benthic algal 

 vegetation from the Atlantic, so that the Pacific coast of North 

 America is very different in this respect from the Atlantic coast. 

 For although in the Pacific the eulittoral may be dominated by 

 species of Fuciis (as well as of Egregia), the lowest portion of this 

 zone is characterized by the unique laminarian Postehia palmaeforrnis 



Fig. 174. — A characteristic Kelp, .4/rt//rt </o//r//o/7;<7(7;/,s' ( ';)• (After Kjellman.) 



(Fig. 172) on rocks exposed to heavy surf, while the sublittoral 

 contains numerous other Laminariales, often of peculiar form and 

 great size. Examples of these are Macrocystis pyrifera (Fig. 175) 

 and Nereocystis, which are commonly attached on rather deep bottoms 

 10-30 metres down, and may thus be considered as extending the 

 upper sublittoral downwards. However, they possess such a very 

 long ' stalk ' that the fronds, borne at the summit and often accom- 

 panied by air-bladders, can spread out on the surface of the water 

 even at high tide. Such plants thus project their upper parts into 

 the ecological sphere which is most favourable especially in the all- 

 important matter of illumination. 



In southern South America and the less frigid of the austral islands, 

 there may be recognized in the eulittoral an uppermost girdle of 

 various drought-resistant Algae, a middle-to-lower one of surf-re- 



