THE IMPENETRABLE SEA 



each individual soon attains maturity. After a certain 

 number of divisions, what is called an "auxospore" is 

 formed, by which means the diatom's original size is 

 regained. 



What may be termed the ''pill-box" diatoms are only 

 one kind of planktonic plant. The ''boxes" are of all 

 shapes, and not all diatoms are planktonic — there are 

 numbers which are not "wanderers" but are motionless 

 on the sea-beds in shallower coastal regions where 

 light can penetrate down to them. The planktonic 

 (drifting) "pill-boxes" are far more varied in structure, 

 due to the vast variety of devices which assist their 

 flotation. 



Apart from the box-like forms there are diatomic 

 plants which are suspended in the sea water by micro- 

 scopic "life-belts" — tiny globules of oil. Numbers of 

 species live solitary lives, but there are innumerable 

 forms which live in association: linked by their valve 

 surfaces ; or joined in flexible chains by fine threads of 

 protoplasm. 



There are diatomic plants flattened like strips of paper; 

 others which are strung together like pieces of ribbon ; 

 others which are like twisted paper streamers; others 

 which are drawn out into very fine hair-like forms ; and 

 there are rigid needle-like forms, some of them pointed 

 at each end. There are planktonic plants — all invisible to 

 the naked eye — which resemble land insects, such as 

 caterpillars. 



There is one form which roughly suggests the Praying 

 Mantis, and there are many which look like twig- 

 imitating insects — yet all these are plants. Numbers of 

 the microscopic plants resemble household ornaments 

 such as vases or cups, and many of these are beautifully 

 embellished. Myriads of the planktonic plants have 

 flagella with which they draw or propel themselves 

 through the water. Such creatures are enigmas, for many 

 of them are claimed by both botanists and zoologists, and 



240 



