156 



Aquatic Organisms 



and pools. The common water weed, Phil0tria, (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 are found here. 

 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, 



FIG. 66. A leaf of the white water-crow- 1 . - r 1 



foot, Ranunculus. which f orm 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 Pontederiaceae, 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 

 Droseraceae, 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 



