THE BEGINNINGS OF PLANT LIFE 9 



exposed water is to be found, diatoms may be 

 looked for, whether it be stagnant or running, 

 salt or fresh, warm or cold. Even the melting- 

 snow on the summits of the highest mountains, or 

 the water that lodges in your rain-water spout, 

 frequently contains diatoms in abundance. 



As the water evaporates, these invisible plant 

 particles become dry, and by reason of their 

 lightness and tenuity get wafted, still alive, from 

 one region to another bv the hioh winds. The 

 hottest sun and bitterest cold does not affect their 

 vitality. As the air calms they settle down again, 

 and after months of frost or scorching sun, given 

 moisture and sunlight, they again rapidly multiply, 

 and so become distributed everywhere. 



When considering the desmids 1 mentioned 

 that the cell-walls sometimes developed spines 

 or markings on their surface. Now diatoms 

 present most extraordinary and remarkable 

 features in this respect. Each little vegetable cell 

 that constitutes a diatom has the power to absorb 

 from the surrounding water that chemical com- 

 bination termed " silica " or flint, a small proportion 

 of which exists dissolved in most natural waters. 

 The silica which it thus appropriates becomes 

 deposited regularly on the cell-wall, and so the 

 sino-le veo'etable cell becomes clothed with an 



o o 



almost indestructible Hinty armour. But this is 



