572 A TEXTBOOK OF BOTANY [Ch. XIV 



Allied is the form of Papyrus (Fig. 375). Such reeds can live 

 in deeper water than any other except the floating helo- 

 phytes. Water Grasses; like the last physiologically, 

 but more leafy ; typified by Wild Rice. Waterside Herbs ; 

 long-petioled leaves from underwater roots or rootstocks; 

 typified by Pickerel Weed, Water Plantain, Arrowhead, and 

 by Calla in its native home. Dimorphic-leaved Herbs; 

 air-fitted leaves above water, and water-fitted beneath the 

 surface, on the same stem ; typified by Bidens Beckii (Fig. 

 32), some species of Ranunculus, and Cabomba. Aeren- 

 chymous Herbs; possessing special organs of aeration as 

 in Jussicea (Fig. 176). Floating Leaf Aquatics ; typified 

 by the White and Yellow Water Lilies; large, rounded 

 leaves, unwettable on the upper surface, are connected with 

 the submerged rootstocks by elongated flexible petioles, ad- 

 justed to the depth of water, and specially fitted for con- 

 duction of air through the large passages. Water Poppy, 

 some Knot-weeds, and Water Shield belong here. Related 

 is the form of our Wild Calla, and the Buck Bean in which 

 the shoots are afloat. Free-floating Aquatics; either a 

 thallus, as in floating Liverworts (Riccia, page 480), or a pel- 

 tate shoot, as in Lemna (Fig. 379), or floating leaves, as in 

 Salvinia and Azolla (Fig. 353), or a rosette, as in Water 

 Hyacinth (Fig. 380). In all cases the upper surface is un- 

 wettable, and the roots hang below as a counterweight 

 which prevents overturning. Floating Bog Mosses; 

 typified by the Peat Mosses (Sphagnum species, page 485), 

 which grow out over water as mats, and later grow up on the 

 peat which they form. 



No prominent helophytic trees or shrubs have been 

 developed, unless the Bald Cypress of southern swamps, with 

 its aerating knees (page 252) is here included. The 

 swamps and flat bogs of temperate regions are occupied 

 mostly by evergreen conifers, or by heath shrubs, though 

 the mode of aeration of their roots, aside from their nearness 

 to the surface, is somewhat uncertain. These forms seem to 



