Handbook of Paleontology , 89 



some species in each section extending beyond the limits 

 of that section. In general, Cape Cod and Cape Hatteras 

 mark the southern and northern limits, respectively, of 

 the arctic and tropical floras. Arctic forms are not gen- 

 erally found south of Cape Cod, nor do many tropical 

 forms pass north of Cape Hatteras. 



Seaweeds have special habits, and certain climates and 

 seasons are required for their growth. Sandy beaches 

 are unfavorable to their growth, but such beaches will be 

 found strewn with many varieties of seaweeds washed in 

 from deeper waters, particularly by storm waves. Sea- 

 weeds love best the rocky shores and are most abundant 

 there, particularly where the nature of the rock provides 

 numerous crevices that give shelter from the waves. 

 Beautiful varieties and many of the more delicate species 

 are found in the tide- pools, among them some of the red 

 algae. Seaweeds, likewise, have a lateral or vertical zon- 

 ing into three belts, the strand, the laminarian and the 

 coralline zones. This subject will be only briefly touched 

 upon here, but will be treated more fully later in connec- 

 tion with the discussion of the animal associations of the 

 shore. The seaweeds of the strand zone, or area between 

 the tide marks, are alternately exposed to the sun and air 

 and complete submergence. Species of the very gelati- 

 nous Rockweeds (Fucus) are very plentiful here because 

 nature has provided them with the means to withstand the 

 extreme conditions they must undergo. Fucus and an- 

 other of the brown algae, Enteromorpha, predominate in 

 this zone. The laminarian zone comprises the area be- 

 tween the low- water mark and a depth of 15 fathoms. 

 Here grow some of the beautiful red algae (Florideae) 

 and brown algae (Laminariaceae). The coralline zone 

 extends from the 15-fathom depth to a depth of about 50 



