124 THE WATERLILIES. 



fruit is pressed close against the mud. N. tetragona resembles N. /lava 

 in these respects. In deep water (i to 5 meters) N.flava, odorata, alba, 

 and tnbcrosa, carry the spiral turning to its highest development. From 

 a few centimeters above the rhizome to within a few centimeters of 

 the flower, the peduncle is coiled into a close helix from 2 to 8 centimeters 

 in diameter, and with 2 to 8 or 10 turns ; thus the fruit is drawn down 

 within about half a meter of the bottom of the water, and often quite 

 into the mass of algae and other vegetation overlying the mud. Just 

 such an adaptation has given the specific name to Vallisneria spiralis. 

 Besides removing the fruit from the drying influence of the air, the 

 purpose of these movements is doubtless twofold : First, to hide the 

 fruit from the many aerial, aquatic, and amphibious animals which might 

 feed upon it, for the majority of such creatures get their food at the 

 surface rather than in the depths of the water ; secondly, to reduce the 

 danger of the fruits being broken off, as would easily occur with the long, 

 slender peduncles of Castalia. 



