SECT, ii. MARINE CONFER VJE. 2 2 1 



The structure of tlie marine Algse is entirely cellular. 

 Deprived of vascular tubes, they can have no circulation 

 of sap, consequently they derive their nourishment by 

 absorption throughout their whole surface from the 

 medium in which they live, for their root, or rather 

 fulcrum, only serves to fix them to the rocks and stones 

 to prevent them from being buffeted by the waves. 

 Since solar light and heat decrease rapidly with the 

 depth, each family of Algse has a zone peculiar to itself. 

 The first zone extends from high to low water mark, and 

 is inhabited by plants periodically exposed to the atmo- 

 sphere, to the direct light and heat of the sun, and occa- 

 sionally to rain. Some of the Agse that are long left 

 dry are believed to derive some nourishment from the 

 substances to which they are fixed. The second zone, 

 which extends from low water mark to a depth of 

 fifteen fathoms, is the region of the great marine forests 

 which encircle the globe in both hemispheres. Other 

 two zones follow at greater and greater depths, but all 

 are divided into various minor regions, below the last 

 of which the Algse decrease as the depth increases, till, 

 as far as we know, vegetation ceases altogether; that 

 depth, however, must be very great, as diatoms are 

 sometimes found, and in great quantities, three hun- 

 dred fathoms deep. 



The marine Confervas, like those growing in fresh 

 water, are slender-jointed filaments formed of one series 

 of cells joined end to end. The cells become more or 

 less flattened on the surface of contact, while the side 

 walls retain their natural curvature, which may be cylin- 

 drical or oval. The filament may, therefore, be cylin- 

 drical or beaded. The cells are almost always longer 

 than they are broad, and for the most part equal and 

 similar in the same plant, although there are exceptions 

 to uniformity of size. The cells contain a transparent 

 liquid through which minute solid particles of various 



