Chap. II] 



MARINE VEGETATION 



793 



are occasioned by differences in illumination. The change in the flora, 

 corresponding to the reduction in the light as the depth increases, is here very- 

 marked. It is repeated to a certain extent in the horizontal direction in corre- 

 spondence with the manifold degrees of light and shade caused by the irregu- 

 larity of the coast. Yet not all the deep-sea forms appear on equally 

 illuminated stations near the surface. The shade-species are, as every- 

 where, Rhodophyceae, such as species of Lithophyllum, Lithothamnium. 

 The Phaeophyceae, on the contrary, chiefly prefer bright spots. The 

 umbrella-shaped green Acetabularia mediterranea (Fig. 482) and the disk- 

 shaped brown Padina Pavonia belong to the most marked sunlight- 

 loving Algae. Even some Florideae, for instance species of Laurencia 



Fig. 481. Caulerpa prolifera. a Growing-point. 

 b Young lobe of thallus. r Khizoids. Half 

 natural size. From Strasburger's Text-book of 

 Botany. 



FlG. 4S2. Acetabularia me- 

 diterranea. Natural size. 

 From Strasburger's Text- 

 book of Botany. 



and Ceramium, display a marked preference for light ; in such cases 

 they have dull tints, and only when accidentally growing in the shade 

 do they assume the bright red tints that distinguish their photophobous 

 allies. 



Sensitiveness to light has called forth in Mediterranean Algae — and 

 probably in those of all seas of low latitudes — adaptations which are not 

 absent from colder' seas, but are less strongly developed because of the 

 lesser intensity of the light. The contrivances protecting Algae from 

 excess of light, as described earlier in this work x , were all observed by 



1 See p. 58. 



