A WIDE WORLD OF PLANT-LIFE 31 



they are so tiny that if a hundred of them were sprinkled 

 on a piece of clear glass, and you were to hold up that 

 glass against the light, you would see nothing. Yet the 

 Diatoms would be there. 



Real living water-plants are they ; each one enclosed 

 in a minute case or box, made of a flint-like substance, 

 in two halves which exactly fit one another like a box 

 and lid. The outside is decorated in all sorts of patterns ; 

 one kind having one pattern, and another kind another 

 pattern. About two thousand different species are 

 known; each particular species being marked with its 

 own special design, unlike all the rest. The beauty 

 and finish of these ornamental markings are marvellous.^ 



For thousands of years nobody knew anything about 

 the Diatoms and their wonderful little boxes. It was 

 not till men had learnt how to make microscopes that 

 the Diatom-cases could be seen at all. 



Somehow these living specks travel about; and 

 probably it is by means of very fine lashes — called 

 cilia — put out through little holes, and used like oars 

 for rowing themselves along. 



A step or two higher up the ladder brings us to the 

 small and dainty Volvox plant, which may be found in 

 many an English pond. It is greenish in colour, and 

 globe-like in shape; and it too moves about like an 

 animal, rowing itself along by means of little arms or 

 cilia. It really is not one plant only, but a whole 

 colony of plantlets, all pressed together and joined into 

 one, and surrounded by a kind of envelope. 



1 For illustrations of these Diatom-cases see The Romance of 

 the Mighty Deep, by the same author : opposite pages 154, 156. 



