50 THE BOOK OF NATURE STUDY 



in water. The majority of aquatic plants protrude their flower- 

 ing stems above the water in order to produce flowers and 

 make seed ; the Water Plantain, the Arrowhead, and many 

 others will not flower if completely submerged, whilst the Awl- 

 wort when completely submerged forms cleistogamous flowers, 

 i.e. flowers which never open and are self - pollinated. There 

 are only about fifty Flowering Plants adapted for pollination 

 and fertilisation in water. The Grass- Wrack (Zoster a), a marine 

 plant abundant in the brackish water of lagoons and off muddy 

 seashores, has peculiarly formed pollen. The outer coat character- 

 istic of the pollen grains of land plants is absent ; the anthers 

 open under water, and as soon as the pollen cells are liberated 

 they take the form of long cylindrical tubes, which are carried 

 by the water to the stigmas of the pistillate flower. The Naiad 

 have pollen of the same character. Those aquatic plants which 

 discharge their pollen above the surface of the water have pollen 

 grains with the usual outer coat, and they are round or elliptical, 

 not cylindrical or tube-like. 



For the dispersion of their fruits and seeds, aquatic plants are 

 frequently provided with means of floating. Schimper mentions 

 a definite floating bladder in the case of the Morinda citri folia, 

 but the majority of these aquatic plants merely have fruits with 

 tissues containing plenty of air spaces, which make them light 

 and buoyant and able to float great distances. The double coco- 

 nut of the Seychelles Islands has been found on the coast of Su- 

 matra 3000 miles distant ; the fruits of the Soap-Berry (Sapindus 

 Saponaria) have been brought to Bermuda by the Gulf Stream 

 from the West Indies, and the West Indian bean, Entada scandens, 

 has travelled as far as the Azores, about 3000 miles. Facts of this 

 kind are of peculiar interest, as they explain the resemblance of 

 the shore flora of such widely separated land as the Malay 

 Archipelago and the Central Pacific islands. 



The coco-nut bought in England gives no idea of the tissue 

 by which the fruit floats. The fibrous covering has been stripped 

 off to be made into ropes and other articles of commerce, and 

 what is bought is usually the hard shell with the white endosperm 

 inside. It is this husk of fibrous tissue with plenty of air spaces 

 in it which enables the nut to float these immense distances ; 



