THE ECOLOGY OF PLANTS. 419 



produced at the ends of the branches. These buds are large 

 and their leaves contain reserve food; they drop off and 

 remain at the bottom until spring. Buds of this kind occur 

 in Water Milfoil, Hottonia, Frog-bit, Bladderwort, and various 

 species of Potamogeton (Pondweed) . 



What we may term "typical" aquatics grow with the 

 whole shoot (except, in most cases, the flowers) under water 

 and the leaves submerged or floating. Some plants can grow 

 either submerged or on muddy soil with their shoots in the 

 air ; in these amphibious plants the leaves of the land form 

 are broader and the stem and leaf structure resembles that 

 found in marsh plants. Many water-loving plants can be 

 grown on land, either by transplanting them to soil or by 

 sowing the seeds in soil : in the former case the new shoots 

 formed differ from the water form with regard to leaf shape 

 and leaf and stem structure, in the latter case the seedlings 

 usually produce at first some leaves of the aquatic type and 

 later bear broader land-leaves. This change occurs frequently 

 in nature, when a pond becomes more or less dried up in 

 summer; observations should be made on these* "amphi- 

 bious " plants. 



Experiments should be made on the lines suggested, and 

 also the reverse kind of experiment, i.e. transplanting, or 

 germinating the seeds of, land plants in mud, very wet soil, 

 or in water. In some cases the change Icrom land form to 

 water form can readily be brought about, especially with 

 plants which grow ordinarily in damp places. 



Since water plants reproduce themselves extensively by 

 vegetative methods, they flower, on the whole, less freely than 

 land plants often only when the water has sunk low or the 

 plants have got on to muddy soil. In a few cases the flowers 

 are adapted for pollination at the surface, or even under 

 water. In Vallisneria (not a British plant, but often grown 

 in aquaria) the male flowers break off when mature, as buds, 

 and float up to the surface, where they open and expose the 

 anthers. The female flowers, which are on separate plants, 

 open about the same time and have long stalks which bring 

 them to the surface, where the stigmas frequently come into 

 contact with the floating male flowers (Fig. 175). 



In the Eel-grass or Grass-wrack (Zostera), the pollen-grains 

 are threadlike and have the same specific gravity as the 



