336 DIP^ECTIONS FOR THE MICROSCOPE. 



" These capsules may be kept in the water for several days without 

 any further perceptible change. When that is dried up they return to 

 the opake state, and the same operation may be several times repeated 

 on them. 



" In exhibiting this spectacle to some friends, pure water not being 

 just at hand, a drop of brandy was substituted for it. This gave rise 

 to a phenomenon equally curious and unexpected. The grains expand 

 as in the water; but in the mean time they are put into rapid motion, 

 each grain darting from side to side with the vivacity of a swarm of 

 gnats in the air. As they approach to complete expansion the motion 

 dies away, and one after another sinks to the bottom. By a small ad- 

 dition of fresh brandy some few are e>;cited a second time, but with 

 fainter movements. Presently the liijuid begins to be ol)SCured, and in 

 a few minutes the grains are mostly dispersed anddccom[)osed,and the 

 spirit exhaling, leaves a sort of extract on the glass mixed with many 

 undissolved particles, among which sometimes appear a few unbroken 

 grains, much changed, and now resembling an empty bladder lying 

 riat." 



Mr. Howard, after the same experiments on various other plants, 

 observes, " The proper sjiirit for this purpose seems to be a mixture of 

 one part of pure spirit of wine with two of water. A stronger spirit or 

 spirit of wine alone may sometimes be required, when we operate 

 upon a pollen which has by any means become previously saturated 

 with moisture, (or has lost, by keeping, a part of its irritability,) but it 

 does not enter the dry grain so readily as water alone. 



" It is proper here to remark, that the utmost care is requisite to 

 prevent accidental mixtures of the subjects or menstrua in these ex- 

 periments, which might greatly embarrass and mislead the observer; 

 separate pieces of clear glass for the several kinds, and separate point- 

 ed glass tubes to convey the liquids, will tlu rcforc be requisite. It will 

 be proper attentively to examine the ])ollen dry, as well as tlie liquids 

 before they are used, in order to be satisfied of the absence of animal- 

 cules and other extraneous matter which might be suspected to in- 

 fluence tlie appearances. 



" I do not pretend to say that the above-related experiments were 

 absolutely free from optical deception; but I may venture to affirm, 

 from frequent repetition of them, that when tried with due precaution,, 

 thev will scarcely ever be found to fail of producing the appearance re- 

 lated." 



MINERALS. 



Ciystuls. — The name Crystal is given to those polyhedral hodie.% 

 produced by nature and the operations of chemistry, which i>ubsess a 

 reralar gcoiuetrica! form and rectilineal interior btructurc. 



