SEEING BY AID OF THE LENS. 



20^ 



them, and the waving' plume-like ap- 

 pearance of a filamentous body covered 

 in this way is often very elegant." 



The brooks about West Point are no 

 exception. The writer has seen a sim- 

 ilar mass of different diatoms so densely 

 covering a space a hand-breadth wide, 

 that it was collected by the spoonful, and 

 on a microscopical examination proved 

 to be a natural culture, with absolutely 

 no admixture of other diatoms or of any 

 other microscopic object. In a past geo- 

 logical age (Tertiary) diatoms in the 

 greatest and most beautiful varieties have 

 so flourished, that they now form depos- 

 its thirty or tortv feet in thickness and 



estimated that a cubic inch of a similar 

 deposit, contains about forty-one thous- 

 and millions of these organisms. 



A motile microscopic object naturally 

 suggests animality, as motile plants seem 

 to he uncanny things, and not to be ac- 

 cepted without protest. Diatoms have 

 not escaped that fate, since some, not all, 

 are spontaneously motile, although mi- 

 croscopists at the present day believe that 

 they are plants. If a perambulating 

 diatom has its freedom, it will myster- 

 iously advance directly forward until it 

 meets an obstacle, when some forms will 

 hesitate, push, and then retreat, to ad- 

 vance again in another direction ; others, 



^^m^ 



Fig. 4. Fig. 6. 



DIATOMS. 

 Selected to show variety of form and of sculpturing 



Fig. 8. 



man} - miles in extent. The city of Rich- 

 mond has underlying it such a bed of 

 fossil diatoms thirty feet thick. The 

 artesian wells of Atlantic City, at a depth 

 of five hundred feet pass through a simi- 

 lar deposit, as the researches of Air. 

 Lewis Woolman have shown. Other 

 beds of such plants are known in Alary- 

 land and in Xew Jersey, while certain 

 deposits in California and in Xew Zea- 

 land, are world-famous among micro- 

 scopists as containing genera and species 

 not yet found elsewhere. 



In such places these much varied 

 forms lived and died by the billion, for 

 it must be remembered, that while indi- 

 vidually a diatom is, in ordinal'}- circum- 

 stances, invisible to the naked eye, yet in 

 these beds of diatomaceous earth, the 

 number of such plants is so enormous 

 that their dead shells have formed a 

 mass which in aspect resembles grey 

 stone, and must be laboriously dislodged 

 bv the shovel and the pick. It has been 



probably in some way stronger, will con- 

 tinue to press against the obstruction 

 until it is removed, when the plant se- 

 renely resumes its journey. 



The cause of the movement is not well 

 understood. Alan\- theories have been 

 offered to explain it, but none is entirely 

 tenable. It is said to be due to the in- 

 jection and the expulsion of water; to the 

 movements of a thin, fluid mass on the 

 surface of the diatom and in rhythmical 

 motion ; to "the changes resulting from 

 the nutrition of the cell, which must nec- 

 essarily absorb food in a liquid condi- 

 tion," and perhaps to still other causes. 

 Some adherent forms, similar to those 

 referred to by Professor Bailey at West 

 Point, become motile when separated 

 from their point of attachment, a fact 

 that seems to militate against the theory 

 that nutrition is its cause, for the ad- 

 herent forms, as well as those that are 

 permanently free, must likewise absorb 

 liquid food. Air. Cornelius Onder- 



