418 KANSAS CITY REVIEW OF SCIENCE. 



DIATOMS. 



HENRY G. HANKS, STATE MINERALOGIST, CALIFORNIA. 



A diatom is generally admitted to be a single celled plant, bearing a singular 

 relation to the animal and even to the mineral kingdom, being considered by 

 some to belong partly to the latter, and regarded as a vegetable crystal, differing 

 only from minerals in having the power of locomotion, and of multiplying by sep- 

 aration. Kutzing says : "In comparing the arguments which indicate the vege- 

 table nature of the diatomacese with those which favour their animal nature, we 

 are, of necessity, led to the latter opinion." 



In connection with the idea that the diatoms pertain somewhat to the mineral 

 as well as the apimal kingdom, it is a curious fact that silica deposited from fluor- 

 ide of silicon, if crushed between plates of glass and examined microscopically, 

 with a medium power, markings may be seen on the outer surfaces of the vesicles 

 which resemble those of the diatoms, especially pleurosigma and coscinodiscus. 

 It is also remarkable that Dr. James Blake collected fifty species of living diatoms 

 from a hot spring in Pueblo Valley, Nevada, the temperature of which was 163° 

 Fahr. Flint probably originates from diatoms, as does also the silica in certain 

 rocks. 



The name diatom is derived from a Greek word signifying being cut in two. 

 Diatoms resemble the desmids, but differ in having an outer skeleton, or frustule, 

 of silica. The frustule of a diatom is a silicious box, always in two parts, one 

 slipping over the other like a pill box or with edges apposed. The thickness of 

 a single diatom is, roughly, the sixth that of a human hair, and its weight is esti- 

 mated at the 187-1,000, 000th part of a grain. Some varieties attach themselves 

 to other bodies, as the algse, while others swim in the water free. . The study of 

 the diatomacese, aside from their scientific interest, is very fascinating. Their ex- 

 treme and varied beauty is a source of constant pleasure to the microscopist, and 

 the question is often asked. Why is so much beauty veiled from human sight? 



The beauty of the diatoms consists in their color, their general form, and 

 sculpture, or natural marking, which characterize nearly all of them. These del- 

 icate markings are seen under the microscope to be processes, knobs, bosses, 

 concavities, ribs, groovings, and lines, so minute that the highest powers made by 

 the most skillful opticians are required to see them at all ; even then they can only 

 be seen when the apparatus is manipulated by the most skillful operators. The 

 lines of certain diatoms have been measured, and are used to test the magnifying 

 and penetrating powers of object glasses. A slide called a test plate has been 

 prepared on which twenty well known species are mounted, commencing with 

 one on which the lines are comparatively coarse, and ending with one — Amphi- 

 pleura pellucida — which has 130,000 lines to the linear inch. For the convenience 

 of study typical diatoms are mounted on a single glass slide, so arranged that 

 reference can be made to a printed catalogue for the names, while in some cases 

 the names of the species are microphotographed on the slide. 



