THE ECOLOGY OF THE VEGETATIVE ORGANS 

 Inteoddctory 



In view of the fact that Ruppia is a submerged plant, Uving under 

 water at all seasons of the year, and unable to live out of it, a 

 study of the methods by which it accommodates itself to this life 

 is of interest, especially when one compares it with a typical land 

 plant. 



Of course, in a comparison of these two types, the one point of 

 vital importance to be noted first of all is the radical difference in 

 the nature of their environment : the land plant pushes its stem 

 and leaves into the air, a gaseous medium ; while the submerged 

 plant extends its shoots entirely surrounded by water, a liquid medium. 



The striking formal, structural, and physiological dissimilarities 

 which obtain between land and submerged plants have their fun- 

 damental origin in the physical differences of these two media and 

 the concomitant variations in quality and intensity of light, temper- 

 ature, &c. These johysical factors have already been clearly stated 

 by Warming (1902, pp. 127 ff.), Schimper (1898), and others, so that 

 it is unnecessary to recount them here. 



On account of the various methods of ecological classification 

 by different authors, the assignment of Ruppia to a definite ecological 

 group is not as easy as might seem at first sight. Among his four 

 ecological groups Warming (1902, p. 121) defines the hydrophytes 

 as being those plants that are surrounded wholly or for the most 

 part by water, and those that grow in very moist earth. Of the 

 subdivisions of this group the " Enalid society or sea grass vege- 

 tation " includes such plants as Zostera, Cymodocea, Phyllospadix, 

 Potamogeton, Althenia, Ruppia, &c. (1. c. p. 156), 



More recently, however, a tendency has been manifested to re- 

 strict the term hydrophytes to plants of fresh water only (e. g. 

 Atkinson, 1905, p. 484). According to this view Ruppia is excluded 

 and must be classified as a halophyte, an arrangement which seems 

 reasonable, if one accepts the literal meaning of the term "halo- 

 phyte." 



As a matter of fact, a study of the plant shows that the great 

 majority of its adaptive characters fit it for membership in the 

 hydrophytes, and only a few — possibly not more than one or two 

 — features added to its hydrophytic characters would qualify it for 



