198 CECONOMY ©F AQUATIC PLANTS. 



flowers and sinking under water, at night, and rising 

 again in the morning, are conformable to what every 

 body has observed in the Nymphcea. 



But the most memorable of aquatic plants is the Va- 

 lisneria which grows at the bottoms of ditches in Italy, 

 and is not unfrequently found in the rivers of the Uni- 

 ted States. In this the fertile flowers stand on long 

 spiral stalks, and these by uncoiling elevate them to 

 the surface of the water, where the calyx expands in 

 the open air. In the mean while plenty of barren 

 flowers are produced on a distinct root, on short 

 straight stalks, from vvhich they rise like separate 

 white bubbl-s, suddenly expanding when they reach 

 the surface, and floating about it in such abundance as 

 to cover it entirely. Thus their pollen is scattered 

 over the stigmas of the first-mentioned blossoms, whose 

 stalks soon afterwards resume their spiral figure, and 

 the fruit comes to maturity at the bottom of the water. 

 All this Micheli has described, without being aware of 

 its final purpose ; so different is it to observe and to 

 reason ! 



Some aquatic vegetables, which blossom under 

 water, seem to have a peculiar kind of glutinous pol- 

 len, destined to perform its office in that situation. 



The fertilization of the Fig is accomplished in a strik- 

 ing manner by insects, as is that of the real Sycamore, 

 Ficus Sycomorus. In this genus the green fruit is a 

 hollow common calyx, or rather receptacle, lined with 

 various flowers seldom both barren and fertile in the 

 same fig. 1 his receptacle has only a very small ori- 

 fice at the summit. The seeds therefore would not in 

 general be perfected were it not for certain minute 

 flies continually fluttering from one fig to the other, all 



