156 



Aquatic Organisms 



and pools. The common water weed, Philotria, (fig. 65), 

 with its neat little leaves regularly arranged in whorls of 

 threes; and two water crowfoots, Ranunculus, (fig. 66), 

 white and yellow, with alternate finely dissected leaves ; 

 and the water purslane, Ludvigia palustris, with its 

 closely-crowded opposite ovate leaves. 



These are the common plants of the waterbeds about 

 Ithaca. They are so few one may learn them quickly, 



for so strongly marked 

 are they that a single 

 spray or often a single 

 leaf is adequate for 

 recognition. 



Then there are three 

 small families so finely 

 adapted to withstand- 

 ing root submersion 

 that they dominate all 

 our permanent shoals 

 and marshes. These 

 are (i) the Typhaceae 

 including the cat-tails 

 and the bur-reeds, 

 which form vast stretch- 

 es of nearly clear 

 growth, as discussed in the last chapter; (2) the Alis- 

 maceae, including arrow heads and water plantain, and 

 (3) the Pontederiaces, represented by the beautiful blue 

 pickerel-weed. All these are shown in their native 

 haunts in the figures of chapter VI. 



Another family of restricted aquatic habitat is the 

 Droseraceas, the sun-dews, which grow in the borders of 

 sphagnous upland bogs. They are minute purplish- 

 tinted plants whose leaves bear glandular hairs. 



Few other families are represented in the water by 

 more than a small proportion of their species. Those 



Fig. 66. A leaf of the white water-crow- 

 foot, Ranunculus. 



