WATER-LILIES 



101 



surface, by reason of the air which is lodged in their 

 spongy substance. After a day or two the air is dis- 

 lodged, and the heavy seeds sink to the bottom ; some- 

 times the seeds fall from a carpel which is still buoyant. 



Any one who watches the germination of water-lily 

 seeds will find that the young plants pass through a series 

 of changes which per- 

 haps preserve a record 

 of ancient stages of 

 evolution (Figs. 29, 30). 

 The seedling has at 

 first long strap-shaped 

 leaves, like those of 

 Vallisneria and other 

 submerged plants. This 

 form of leaf, though 

 not peculiar to aquatic 

 plants, is well suited 

 to life in a slow current 

 of water. The ribbon- 

 or strap-shaped leaf is 

 succeeded by an ovate 

 leaf, with narrowed 

 base, which reminds 

 us of the aerial leaves 

 of water - plantain 

 (Alisma) or the floating 

 leaves of some common 

 Potamogetons. The 

 next stage is a sagittate leaf like that of arrowhead. 

 Lastly the backward- directed lobes curve inwards till they 

 meet, the long sides become uniformly convex, and the 

 floating leaves of Nymphaea or Nuphar are attained. 

 Such a succession of leaves appears to be normal in water- 

 lilies, and is also exemplified by the Alisma-family, which 

 includes arrowhead and water-plaintain. Its occurrence 

 in two distant families indicates that the succession was 



FIG. 29. Seedling of white water-lily, 

 with primary root, secondary root, strap- 

 shaped leaf and ovate leaf. 



