196 PLANT-LIFE 



into which they are liberated; hence they do not sink 

 or rise to the surface, nor do they swim they simply 

 drift in the slightest current, and thus are specially 

 adapted for conveyance by water movement to the 

 stigmas of the female flowers. 



Other simple, and perhaps primitive, Monocotyledons 

 of an aquatic habit are the Horned Pondweed, Zanni- 

 chellia palustris, found in ponds or lagoons of fresh, 

 brackish, or salt water; Sea Ruppia, Ruppia maritima, ac- 

 commodated to lagoons, salt marshes, and shallow bays 

 almost the world over, common on the British littoral; 

 and various species of Pondweed, Potamogeton, flourish- 

 ing principally in fresh water. To this list we must add 

 the Reed-Maces, Typkacece, with two British species, 

 Typlia latifolia, the Great Reed-Mace, and T. angusti- 

 folia, the Lesser Reed-Mace, both growing on the margins 

 of ponds and ditches, and the Bur-Reeds, Sparganium, 

 with three British species, which flourish on the margins 

 of ponds, lakes, and streams. 



The Aroids, or the Aracese, also exhibit what are prob- 

 ably primitive characters. The best -known British 

 representative is Arum maculatum, the Cuckoo-Pint, or 

 Common Arum (Plate XIII.) ; the Nile or Calla Lily 

 (Calla palustris), cultivated in hothouses in Britain, is 

 also well known. In the Cuckoo-Pint the flowers have 

 no perianth; they are borne naked on a fleshy, club- 

 shaped axis called a spadix, and the whole inflorescence 

 is protected by a specialized leaf, yellow-green in colour, 

 termed the spathe. The club of the spadix is of a livery 

 hue ; the female flowers occur in a series at its base, and 

 the male flowers form another series above them. Above 

 the male flowers is a series of barren flowers with hair- 



