SUPPLEMENT 



coarse, large kelps will stand repeated drying and soaking, and the 

 more delicate plants can be preserved in all their attractiveness. On 

 the rocks at low tide they find the bright green ruffled and translu- 

 cent little fronds of sea lettuce (Ulva) , and perhaps some of the fila- 

 mentous green Algae. The common marine Cladophora has much 

 shorter filaments that the fresh water plant and grows in spongy 

 tufts that are well able to resist the waves. 



Rock weed (Fucus) is the most abundant of the Algse in shallow 

 water. The plant is rarely more than a foot in length, and it has 

 many flattened branches that bifurcate repeatedly ; in the ends of 

 the branches little dots are apparent. The rock weed is not espec- 

 ially attractive, but it grows so near the shore that at low tide it can 

 always be studied on its native rocks, and the tenacity of the holdfast, 

 and the toughness, elasticity and flexibility of its branches tested. 

 Entire plants of Macrocystis are frequently thrown up on the beaches 

 with holdfasts a foot or more in diameter. There are likely to be 

 fragments of many other kelps with interesting holdfasts and air sacs. 

 One kind common on Southern California beaches is the Neyreocystis. 

 The stem is unbranched for many yards and terminates in a great air 

 sac six inches or more in diameter, which floats a whorl of branches 

 with leaf-like expansions. A particularly graceful brown Algae, the 

 sea oak, can be found at the lowest tides growing on the rocks. It 

 has a solid holdfast and the stem soon branches into divisions that 

 resemble lobed oak leaves. Farther up the divisions become a series 

 of air sacs that resemble strings of amber beads. In order to appre- 

 ciate fully the significance of the floaters, one must keep in mind the 

 fact that sunlight as well as chlorophyll is necessary to plants that 

 make their food from inorganic matter. 



Seven hundred feet below the surface of the sea there is absolute 

 darkness, and the zone of vegetation is usually limited to within one 

 hundred feet of the surface. This latter fact is due not merely to the 

 dimness of light. It is easily shown by experiments that, of the rays 

 of different colors and wave lengths that together make up colorless 

 daylight, only the red, yellow and orange rays help in manufacturing 

 the primary organic material. Other rays have the reverse effect, 

 breaking up this material for further changes. Now salt water 

 absorbs the red, yellow and orange rays, that is, it is blue ; so it is 

 well for the larger brown Algae to be held near the surface by the 

 air sacs. 



Our red Algae are much smaller, and those that grow in deep water 

 cannot reach the surface, hence the necessity for the red pigment ; 

 for this pigment has the quality of florescence, that is, of absorbing 



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