124 MARINE ANGIOSPERMS [ch. 



Phanerogams inhabiting the sea were, at that time, less well 



known than most of the higher groups of Algae. These marine 



Angiosperms often grow in 



deep water, and botanists 



have been obliged to depend 



chiefly on the study of casual 



fragments washed up by the 



waves, and thus have been 



apt to miss the organs of 



fructification altogether. 



The marine Helobieae all 

 show a strong affinity, both 

 as regards vegetative habit 

 and reproductive methods. 

 They all have alternating 

 leaves in two ranks arising 

 from creeping stems. Supple, 

 ribbon-like leaves, sessile, 

 sheathing and capable of 

 following all the undulations 

 of the water, are most charac- 

 teristic, occurring in Enhalus^ 

 Posidonia^ Phyllospadix^ Zos- 

 tera^ etc. Several Halophilas, 

 on the other hand, have broad 

 petiolate leaves with Potamo- 

 geton-Vike nervation, while 

 Cymodocea isoetifolia is dis- 

 tinguished by awl-shaped 

 succulent leaves^. 



Submerged pollination 

 and Conferva-like pollen are 

 characteristic of all the 

 marine Angiosperms. The 

 thread-like pollen was figured as early as 1792 by the Italian 



1 Ascherson, P. (1867) and Sauvageau, C. (1890^) and (18903). 



Fig. 83. Cymodocea aequorea, Kon. Plant 

 in the middle of the third year of vegeta- 

 tion ; /= fruit from which plant has grown. 

 (Nat. size.) [Bornet, E. (1864).] 



