154 THE MICROSCOPE AND ITS LESSONS. 



is seen under polarized light for which it has been 

 specially mounted, and we get a bright blue background, 

 with these siliceous crystals in the foreground in a 

 brilliant golden colour, the resemblance to the heavens 

 on a clear night is very striking. This skeleton is in- 

 soluble, being formed entirely of flint, which mineral is 

 abundantly distributed amongst plants. If we examine 

 the ashes of hay or straw after they have been burned, 

 small lumps of what appear to be dirty glass will 

 be found mixed up with them. This is caused by the 

 fusion of the flint (silica) contained in the cuticle com- 

 bining with the potash in the vegetable tissue, forming 

 what is known as "silicate of potash," the scientific 

 name for glass. And this was how glass was first dis- 

 covered. 



In the midst of the cellular tissue of almost every 

 leaf you will see a number of minute crystals called 

 rapMdes (Greek, "needles"). These are beautiful forma- 

 tions, sometimes of phosphates or tartrates, sulphates or 

 carbonates. They are the medicinal properties in all 

 plants. In the onion they are oxalite of lime ; in the apple, 

 malic acid. And here I should like to call your special 

 attention to the medicinal property of an apple, which 

 is a chemical composition of albumen, sugar, gum, chlo- 

 rophyll, malic acid, gallic acid, lime, and water, mixed 

 up in vegetable fibre. It is said that the apple contains 

 a larger percentage of phosphorus than any other fruit 

 or vegetable. This phosphorus is admirably adapted 

 for renewing the essential nervous matter of the brain 

 and spinal cord, for rousing sluggish livers, for neutralizing 

 the effects of unwholesome food, and for the dispersion of 

 chalky matter engendered by eating too much meat ; and 

 for diminishing acidity in the stomach, apples are the 

 finest of all medicines. A good lipe apple is one of the 



