54 6 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 trav- 

 eling 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 mem- 

 ber 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 Tubin- 

 gen, 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 Decem- 

 ber 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 over- 

 looked. 



