32 
they are not subject to any such fluctuations in water-pressure 
and light-intensity as would be the case under the heavy tides of 
the Pacific side of the Isthmus, for in the whole West Indian 
region the range of the tides is for the most part only two or 
three feet. Observations as to the relation of the amplitude of 
the tides to the development of the marine flora in the tropics 
are apparently few and any sweeping generalizations are doubt- 
Fic. 7. Low tide, Bay of Panama. 
less unwarranted, yet it seems probable that the combination of 
wide-ranging tides and a tropical insolation is distinctly unfavor- 
able to any luxuriant growth of marine vegetation. It should be 
added that spermatophytes also, of such genera as Thalassia, 
Cymodocea, Halodule, and Halophila, some of which, as to indi- 
vidual plants, are profusely abundant in most parts of the West 
Indies, especially on a muddy or sandy bottom in moderately 
