EPIPACTIS MEDIA 83 



Fries, was in reality JE. viridijlora Heich., and the first record as a 

 British plant is Leighton's, on the specimens found by him and 

 Babington in 1S35. The subsequent application of the name E. media 

 to specimens of E. latifolia with rugose bosses appears to have been 

 founded on a misapprehension, and the term E. media should now 

 disappear from British botany, except as a synonym of E. atroruhens. 



AQUATIC ANGIOSPERMS : 



The Sign^ificaxce or theie Ststematic Distribftiojt. 



By Agnes Arber, D.Sc, F.L.S. 



It is generally recognized that the primaeval forms of vegetable 

 life were probably aquatic, and that it is only in the highly evolved 

 group of the Seed Plants that a terrestrial habit has become firmly 

 established. It follows that any aquatics met with among the Spermo- 

 phytes must be regarded as descendants of terrestrial ancestors, which 

 have reverted in some degree to the aquatic habits of their remote 

 forbears. That this view is tenable, and that the Aquatic Angio- 

 spernis cannot trace their ancestry in an unbroken aquatic line from 

 some far away algal progenitor, is demonstrated b}^ the fact that their 

 floral organs, in the vast majority of cases, belong to a decidedly 

 terrestrial type. 



From a study of the mode of systematic distribution of aquatic 

 families and species among the Angiosperms, cei-tain general conclu- 

 sions may be deduced. The most obvious and striking feature is the 

 relative paucity of hydrophytes, in comparison with terrestrial plants. 

 Contrasted with those that live on land, the number of aquatic 

 families is so small as to be almost negligible, and even when all the 

 individual hydrophytic genera and species are added, the sum total 

 is relatively insignificant. This result is, however, hardly surprising 

 when we consider that the Phanerogams are essentially a terrestrial 

 stock, and are distinguished from the Cryptogams by their aerial mode 

 of pollination, which has won for them the freedom of the land. Under 

 these circumstances, the reversion to aquatic life could hardly be 

 expected to occur on any great scale. It must also be remembered 

 that the entire area of the fresh waters of the globe is very small as 

 compared with the land surfaces, and that thus the aquatic Angio- 

 sperms occupy a much more restricted field than their terrestrial 

 compeers. 



The mode of systematic distribution of aquatics among the 

 Angiosperms shows every possible variety. Among the Dicotyledons 

 there are cases in which only one species of a terrestrial genus is 

 aquatic (e. g. Polygonum amphihium^, and others in which a number 

 of species in a genus are h^'drophytic while some are terrestrial 

 (e.g. Banunculus with its aquatic sub-genus Batrachium). Again, 

 an entire genus of an otherwise terrestrial family may be aquatic 

 (e. g. Hottonia among the Primulacese) , or several genera of family 

 may be aquatic (e.g. Jussieua, Ludwigia, etc., among the Ona- 



