the Marine Algce of the Firth of Forth. 465 



place to Chlorophyceae, where the light is most intense, 

 and most nearly simulates the conditions of ordinary land 

 or clear fresh water vegetation. 



On the general question of depth Meneghini speaks as 

 follows : — " A hundred feet beneath the surface of the 

 sea, living algae are rarely met with, but some are attached 

 to masses detached by accident from higher rocks, and 

 these speedily perish. The number of species decreases 



on descending into the depths of the sea Beyond 



forty feet from the surface, Ulvce are rarely met with ; 

 beyond sixty, there are no Ceramite ; beyond a hundred, no 

 longer Fucoidese, and the vegetable kingdom ceases, leaving 

 the field free for animals, wdiich are always distributed in 

 those abysses with great richness of form and tint." 



Kjellman, whilst asserting that it is at present impos- 

 sible to state the causes of a difference of facies of marine 

 vegetation at different depths, until further advances have 

 been made in vegetable physiology and hydrography, goes 

 on to say : — " Bis auf Weiteres miissen wir aunehmen, 

 dass an der Kiiste von Bohuslau noch bei einer Tiefe von 

 1| bis 2 Faden die Temperatur des Meereswassers, sein 

 Gehalt an fixen Bestandtheilen und an Gasen, der AVasser- 

 druck, die Menge und Beschaflfenheit des bis in diese Tiefe 

 hinabdringenden Liehtes u.s.w. fiir die meisten der Chloro- 

 phyllophyceen und Nostocaceen vortheilhaft sind, dass aber 

 erst in grossere Tiefe diese Verhaltnisse so modificirt 

 werden dass sie den meisten Ehodospermen-Arten ange- 

 messen und gunstig sind." 



It may further be observed generally — 



(1) That many species occur in localities where the 

 external environments are subject to very much greater 

 changes than in other areas. There is, indeed, a regular 

 gradation in this respect (a) from the upper limits of the 

 tide to the bottom of the deeper parts of the estuary, and 

 (h) these changes become more pronounced as the w^ater 

 shallows in the more landward parts. 



(2) Some marine algse have a predilection for condi- 

 tions unsuitable for almost all others, e.f/., Enteromorpha 

 intestinalis, which occurs freely in pools above high-water 

 mark, which acquire their saline constituents from spray 

 only. 



