134 MOUNTAIN AND MOORLAND 



its lower surface 346 stomata, but none on the upper 

 surface. A Water Lily has on each square millimetre 

 of its upper surface 460 stomata, but none on the 

 under surface. The flower of the White Water Lily 

 is very instructive in showing gradual transitions 

 from the petals to the stamens, reminding us that a 

 flower is built up of four sets of transformed leaf-like 

 parts (i) the protective steadying sepals, forming the 

 calyx; (2) the protective attractive petals, forming 

 the corolla; (3) the stamens, which bear pollen-making 

 anthers ; and (4) the carpels, which bear an egg-cell in 

 each ovule. 



Altogether apart from those lake plants of the 

 shore and the floor that we have just spoken of are 

 the constituents of the open-water " plankton " 

 microscopic Algae floating at or quite near the surface 

 and multiplying in prodigious numbers. Diatoms and 

 Desmids and blue-green Algae predominate, including 

 in the last the attractive Oscillarias with remarkable 

 gliding movements. Along with these simple plankton 

 plants there are always microscopic green animals 

 (Infusorians) which have got possession of chloro- 

 phyll and are able to use the sun's rays. We cannot 

 understand the animal life of a lake at all unless we 

 understand that these floating meadows are always 

 capturing the energy of the sunlight and building up 

 carbon compounds by that mysterious alchemy called 

 photo-synthesis, which is the most fundamentally im- 

 portant process in the world. The floating meadows 

 thus form the basal food-supply for higher orders of 

 being in the lake. The unicellular Algae and the 

 green Infusorians are devoured by minute Crustaceans 

 and the like, and these in turn become part and parcel 



