before briefly referred to, and which formerly were regarded as belonging to the animal kingdom—some species of algæ.
In 1843 the botanist Unger, while examining certain green plantfibers under the microscope, suddenly noticed some sphere-like bodies dart out of these fibers and move to and fro in the water, kept in rapid motion through the aid of cilia.
This wonderful sight (for up to this time nothing like it had been observed) surprised him greatly, and he announced his discovery to his collaborators in an essay bearing the title, "The Plant in the Act of Transformation into an Animal."
To the algæ belong those minute organisms that sometimes give to water a bluish-green color, that redden snow, and that change ordinary rain into a rain of "blood." Ehrenberg states that the Red Sea takes its name from the algæ which it sometimes throws far up on its shores. Reports of "blood-rains" are not at all infrequent in the records of the past. Chinese history, written eleven hundred and fifty-four years before the Christian era, makes mention of such a phenomenon; the Bible writers speak of similar occurrences, and Livy also reports an event of this kind.
But only one group of these organisms, the diatoms, will receive our closer attention. They surpass the bacteria in size; still, a good microscope is needed to observe them. Whereas the bacteria present only few, and at that, simple forms, but colors of varied hue, the reverse is true of the diatom family. Their color, when they possess any, is a more or less dark brown or a green, but the delicacy and beauty of their forms is striking. Some look like minute gondolas, others resemble fans, or approach in form an S, a circle, or an ellipse. If a higher magnifying power be employed, most dainty linear tracings will be seen on their shells, for these beings are enveloped in shells which consist chiefly of silica.
Linné's expression, "Natura in minimis maxima" (with her smallest agents Nature accomplishes her greatest works), is especially borne out by the diatoms, for they have been active agents in the formation of the crust of our globe; rocks, ocean-beds, in short, entire geological formations, are the results of their labors. The polishing-slate of Bilin consists only of diatoms—one litre containing something like two billions of them. A considerable part of Berlin, the capital of the German Empire, is built upon a bed of diatoms, the uppermost layer of which is still alive.
Thus far we have noticed the power of locomotion—this prime characteristic of animal life—only in the lower orders of plants, the algæ and fungi. Might we not expect to meet with this also in plants of a higher order? Motion, perfectly free and unrestrained, we should here of course seek in vain, but many plants possess the power of moving some of their parts. In this connection we would recall the Mimosa, which, in response to the slightest touch, will imme-
