CH. xxiii. ORGANIC CHEMISTRY. 193 



cinnamon ; from its roots, camphor ; and from its leaves an 

 oil with the taste of cloves. Then after he had extracted 

 all the juice from the plant, he burnt the dry remains, to see 

 what would be contained in its ashes after the fire had 

 driven off part of the solid matter as gas, and he found in 

 them a kind of salt, which was also different in different 

 plants. But if he poured hot water on the plant before 

 burning it, he found no salt in the ashes, for it had been 

 dissolved and carried off in the water. 



Having now found of what materials the plant was com- 

 posed, the next step was to discover where they came from ; 

 so he took several specimens of earth in which plants can 

 grow and examined them also ; and he found that he could 

 extract from them many of the substances, such as salt, 

 alum, borax, and sulphur, which he had also discovered in 

 the ashes of the plants. It was clear, then, that the plant 

 took these salts out of the earth ; and by a number of experi- 

 ments he went on to prove that they are dissolved by the 

 rain-water which sinks into the earth, and are then sucked 

 up by the plants through their roots and carried up to the 

 leaves, where they are exposed to the air and sunshine, and 

 altered so as to become food for the plant The other 

 parts which did not come from the soil he concluded must 

 be taken in from the air. \ I'hese were splendid facts, and 

 curiously enough a celebrated English chemist, Dr. Hales 

 (born 1677, died 1761), made some similar experiments 

 almost at the same time, which confirmed those of Boer- 

 haave. . Hales even went so far as to measure the quantity 

 of water taken in at the roots and given out at the leaves 

 of plants, and he discovered the way in which plants breathe 

 through the little stomata, or mouths, discovered by Grew 

 (see p. 1 3 81 



From the juices of plants Boerhaave next went on to 



