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THE POPULAR SCIENCE MONTHLY.

exists can be approximately determined; that which gives us the dark lines is denser than the one which gives us the bright ones.

In conclusion, it may be well to point out a difference of some importance between comets and these new stars. A comet, as is generally conceded, consists of a cloud of meteoritic dust traveling round the sun, sometimes in elliptic but more often in a parabolic or hyperbolic orbit; in other words, those traveling in elliptic orbits have been captured by the sun and return to it periodically, while those pursuing a parabolic or hyperbolic orbit after one passage near the sun are forever lost to us.

Thus a comet with an elliptic orbit may be said to be a member of the solar system, and on this account can approach very near to our earth; and in fact our earth has even passed through one, giving rise to the phenomena of a great number of shooting-stars.

A new star, on the other hand, never approaches our system, but is formed at very great distances from us, distances probably as great as that of the nearest star, so that light, which travels one hundred and eighty-six thousand miles per second, takes about thirty years to complete its journey to us. Our new star, then, is already old.—Saturday Review.

 

THE DISCOVERY OF THE SEXUALITY OF PLANTS.

ATTENTION was called, at one of the late meetings of the Brandenburg Society of Botanists, to the fact that the two hundredth anniversary of the discovery of sexuality in plants had recently occurred. It was in fact two hundred years since the doctor and botanist Rudolf Jakob Camerarius, professor at Tübingen, separated two feminine types of the annual mercury from a group of plants of the same kind growing in a garden, and remarked that they had hollow seeds. His report on this subject, published in the Ephemerides of the Leopoldine Academy, is dated December 28, 1691. Camerarius demonstrated that plants are reproduced like animals by means of sexual organs. Till then confused notions had been entertained on the subject, and no one had thought of submitting it to an experimental test. Camerarius found that the stamens constituted the male organ and the pistils the female organs, and published the fact in his memoir De Sexu plantarum Epistola. The thought, like many other great discoveries that are not appreciated at the time, was too remote from current ideas to be accepted, and was comparatively overlooked.