Marvels of the Universe 



395 



page 3q6, in which the little holes are so 

 small that fift\- thousand would have to 

 be placed side by side to reach across a 

 halfpenny. 



In the foregoing remarks we have dealt 

 with the Diatoms chiefly from the micro- 

 scopist's point of view, that is to say with 

 the hard flinty skeleton or support for the 

 living gelatinous envelope. It is the enve- 

 lope that has chief interest for the botanist, 

 for that is the only part that has life, and 

 by its vital activity it e.xtracts the dissolved 

 flint from the water and deposits it in a 

 solid form within its own simple body. We 

 say simple body advisedly, for the Diatoms 

 are among the simplest of all the plants — 

 those that consist of a single cell. They never 

 reach a higher development than this and 

 though a Diatom that is multiplying by 

 division may be said to consist temporarily 

 of two cells, it does not remain long in this 

 condition. In certain species a number of 

 Diatoms ma}' be seen united in a chain, 

 but each link is a separate and complete 

 plant. 



!More than ten thousand distinct species 

 of Diatoms have been named and described. 

 As already indicated, they are ubiquitous. 

 They occur in such vast numbers in the 

 living state as to form a brown scum on 

 stagnant water. They sometimes cling in 

 thousands to the stems and leaves of higher 

 freshwater plants and to seaweeds. They 

 may even be collected from the face of wet 

 walls and rocks. 



One more remark should be made 

 before closing this brief account of one of 

 Nature's marvels. Some of these plants 

 possess a power of movement which has 

 baffled aU attempts at explanation, several 

 theories having been put forward : but all 

 seem open to certain objections. To 

 examine this movement it is only necessary 

 to gather a little mud out of a pond, when 

 several varieties will be sure to be obtained ; 

 and no little surprise will be felt at seeing 

 some of these minute organisms floating 

 across the field of view of the microscope 

 in a slow but elegant manner. 



o. 









Phrilo lilj] 



[Miu- Poser, F.R.M.S. 



A DIATOM. 



This photograph of one of the " Little Ship " section of Diatoms 

 is ahout 7 50 times larger than the natural size. 



