156 THE MICROSCOPE. Oct. 



to consist of myriads of little spheres, most of them hav- 

 ing four radiating arms. Now, while you are observing, 

 breathe very gently over the glass slip, or better have a 

 friend do this for you, and suddenly all the arms will 

 contract about the spheres as if you had breathed into 

 them a very spasm of life. !f^ow watch the spores care- 

 fully a few seconds longer and you will see the arms 

 gradually unfold again in quite a comical, cautious way. 



The explanation of this peculiar power of the horse- 

 tail spores is not far to seek. The little arms are ex- 

 ceedingly hygroscopic and they expand very promptly 

 to the moisture of the breath. Indeed I was greatly 

 amused one day while observing their antics to see them 

 keep '"p a slow waving twisting motion as though they 

 were undecided as to whether they should remain ex- 

 panded or fold about their precious charge. This puz- 

 zled me until I observed that the door to my room was 

 open; and as the air outside was more moist than in 

 doors, every little current as it came and went registered 

 its influence on those sensitive little arms. 



Each arm may be seen to have a spoon-shaped extrem- 

 ity which enabled the arms to cover the spore com- 

 pletely while yet green. Indeed, they then constituted 

 the outer coat. As the spore ripens, its outer coat splits 

 up into these arms and a dry wind readily detaches it 

 from the spore case, bears it aloft and away until per- 

 chance it is wafted over a swampy place when the air 

 is moist. The moisture causes the arms to fold about 

 the bit of concentrated life in their charge, allowing our 

 little aeronaut to settle in a congenial place when it may 

 multiply and replenish the earth with horse-tails. 



Soluble Glass as a Mounting Medium. — Soluble glass 

 sufficient to cover the specimen is used, the cover-glass is placed 

 in position, and a hard brown varnish applied round the edge 

 to fill up the intervening space under the slip, and so act as a 

 cement to keep the cover-glass firmly fixed. — W. W. McBride. 



