CHAPTER II 

 MARINE VEGETATION 



Introduction. Families composing the marine flora, i. The Benthos, i. Genoa!. 

 Lithophytes, sand-plants, mud-plants. Epiphytes. Photic region : emerging belt, sub- 

 merged belt. Horizontal differentiation, ii. The Benthos of Tropical Seas. Sargassum. 

 Poverty in plants belonging to the emerging belt. iii. The Benthos of Warm Temperate 

 Seas. Differentiation in the Bay of Naples according to Berthold. Predominant signifi- 

 cance of light. Periodicity of light and periodicity of movement, iv. The Benthos of Cold 

 Temperate Seas. Preponderance of brown Algae. Emerging and submerged belts. 

 Reduced influence of light. Temperature and periodicity. Change of fronds. South 

 temperate seas. v. The Arctic Benthos. Great luxuriance. Role of the Fucaceae and 

 Laminariaceae. Habitats. Periodicity. 2. The Pelagic Plankton. Systematic com- 

 position. Oecological characteristics. Regions of illumination. Climatic zones. 



INTRODUCTION. 

 THE marine flora includes only a few phanerogams, the so-called sea- 

 grasses (Fig. 476), which are all confined to the benthos and belong to 

 two families, Potamogetonaceae and Hydrocharitaceae. 



The Potamogetonaceae l are represented by five species of Zostera, two of Phyllo- 

 spadix, two of Posidonia, one of Ruppia (rather brackish), seven of Cymodocea, and 

 two of Halodule. The marine Hydrocharitaceae are several species of Halophila, 

 one of Enhalus, and two of Thalassia. 



Pteridophyta and Bryophyta are entirely absent from the sea. The 

 main mass of the marine vegetation is formed by Algae, which belong 

 to the most diverse classes and orders. The largest Algae, comparable 

 with vascular plants and mosses in dimensions and structure, are Rhodo- 

 phyceae, Phaeophyceae, and a few Chlorophyceae. They all belong to the 

 benthos. The small Algae, just visible or invisible to the naked eye, 

 are chiefly Cyanophyceae (Oscillarieae), Diatomaceae and Peridineae, with 

 fewer green Algae (Protococcaceae and others). Such microphytic Algae 

 form the main mass of the vegetable plankton ; they are, however, also 

 richly represented in the benthos. Fungi are represented in the sea by 

 only a few microscopic forms. Bacteria are very abundant in shallow 

 water near the coasts, but scanty in the open sea ; they are partially 

 responsible for the phenomenon of marine phosphorescence. 



1. THE BENTHOS. 



i. GENERAL. 



The plants composing the marine benthos are very largely lithophytes. 

 Their massive forms are fixed to the substratum by strong adhesive disks 



1 See Ascherson, I, II. 



