thousands of them and a great many different forms—though it is quite easy to find them almost everywhere, it is still very difficult to make out their manner of existence. For example, how they perform the feat of locomotion is not well understood. There are two ways of explaining this: one is, that the diatom moves from place to place, owing to the osmotic changes constantly taking place inside the shell; the other and perhaps better authenticated opinion is connected with the peculiarity already referred to—that is, the presence of little apertures in the wall through which portions of the protoplasmic contents protrude. Those who believe 
Fig. 5.—Stictodiscus Californicus. in the osmotic theory claim that no such apertures exist, and consequently no protoplasm finds its way to the outside of the shell. In connection with this point comes the story of the visit.
While working in the Botanical Laboratory of Berlin this past summer, the writer was invited to visit a gentleman having the reputation of knowing more about diatoms than any other person now living. It is rather a strange fact that this gentleman is not a learned professor who has spent a long life over scientific problems, but a retired book-seller who owns a beautiful villa in the suburbs of Berlin, and has for many years been gathering information of various kinds about this wonderful little plant. He has nearly all the literature treating this subject, several large volumes of which are now out of print, and for which he told me he had been obliged to pay exorbitant prices.
Before proceeding to the inspection of the laboratories, specimens, models, etc., coffee and cakes were served in the garden, a distinctively German hospitality which no scientific interests are allowed to interfere with. We then began in the preparing laboratory, a small but very completely fitted room, where the material for investigation is stored, treated, and classified for use. Here are the chemicals used in preparing the plant for examination. Some processes serve to preserve the form and general structure of the living part within the shell, so that this may be studied; other reagents, on the contrary, destroy the living portion, whereby the shell may be more easily examined. In this laboratory was a microscope of somewhat older style than our recent ones, but a very good, reliable instrument, which he told me
