THE STEM AKD THE LEAF 



67 



with sleet (Fig. 28). These may be blown over crusted snow 

 or floated along by brooks or rivers near which the trees 

 grow, and doubtless often lodge in spots where they take root 

 and grow into new trees. 



61. Aerial, floating, and submerged leaves of water plants. 

 Many plants which grow rooted under water have only aerial 

 leaves. To this class belong many arrowheads, the cat-tails, 



FIG. 55. Victoria regia and other tropical and sub-tropical water lilies at 

 the nurseries of Henry A. Dreer, Philadelphia 



The Victorias have the largest known floating leaves, sometimes six feet in 

 diameter and, like rafts, capable of supporting large water birds 



wild rice, pickerel weeds, and other familiar species. A few 

 common plants like the pond lilies and Victorias have floating 

 leaves only (Fig. 55). Some water crowfoots and pondweeds 

 have all their leaves submerged, while other species of these 

 plants and some arrowheads have part of their leaves ex- 

 posed to the air and others wholly under water. 



Submerged leaves are often made up of many thread-like 

 divisions, apparently to enable them to present as much 



