STEPHEN HALES 125 



Cedar of Lebanon, to the Hyssop that springeih out 

 of the wall : So it will not, I presume, be an un- 

 acceptable entertainment to your Royal Highness," 

 etc. 



But the real interest of the dedication is its clear 

 statement of his views on the nutrition of plants. 

 He asserts that plants obtain nourishment, not 

 only from the earth, "but also more sublimed and 

 exalted food from the air, that wonderful fluid, 

 which is of such importance to the life of Vegetables 

 and Animals," etc. We shall see that his later 

 statement is not so definite, and it is well to rescue 

 this downright assertion from oblivion. 



His book begins with the research for which he 

 is best known, namely that on transpiratioik. He 

 took a sunflower growing in a fl6\veF-pot, covering 

 the surface of the earth with a plate of thin milled 

 lead, and cemented it so that no vapour could pass, 

 leaving a corked hole to allow of the plant being 

 watered. He did not take steps to prevent loss 

 through the pot, but at the end of the experiment 

 cut off^ the plant, cemented the stump, and found 

 that the "unglazed porous pot" perspired 2 ozs. in 

 12 hours, and for this he made due allowance. 



The plant so prepared he proceeded to weigh at 

 stated intervals. He obtained the area of the 

 leaves by dividing them into parcels according to 

 their several sizes, and measuring one leaf- of each 

 parcel. The loss of water in 1 2 hours converted to 

 the metric system is 1.3 c.c. per 100 sq. cm. of 



^ This he does by means of a network of threads J inch apart. 

 Pfeffer, Pf.anzenphysiologie, ed. i, i. p. 142, recommends the method 

 and gives Hales as his authority. 



