236 Britain's Heritage of Science 



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was dependent upon its exposure to air, but he missed the 

 fact that the green colouring matter is dependent upon light. 

 He had noticed that many vegetable juices were turned 

 green by the addition of alkalies, and he considered that some 

 alkaline properties of the air produced the well-known colour 

 of leaves. He was groping after the fact that air was necessary 

 to a plant for its nutrition, though his ideas were by no means 

 definite. On the whole his greatest contribution to Science 

 is his discovery of the sexuality of plants; but that is at 

 least equalled or more than outweighed by his general contri- 

 butions to our knowledge of the anatomy of plants and to 

 the science of Botany in almost all its aspects. 



The last half of the seventeenth century is distinguished 

 by the two names of Ray and Grew. Ray, unfortunately, 

 had no successor. Stephen Hales, with whom we now deal, 

 was the solitary follower of Grew until comparatively modern 

 times. 



Stephen Hales (1671-1761) was born in Kent and belonged 

 to the same family as Sir Edward Hales, titular Earl of 

 Tenterden, the well-known Royalist. He was educated at 

 Corpus Christi College, Cambridge, where he was admitted 

 a Fellow in 1602-1603. As a resident of Cambridge he 

 " scoured the fields for Ray's plants," and worked in the 

 " laboratory at Trinity College." 



In 1708-1709 he became perpetual curate of Teddington, 

 Middlesex, in which parish, although he held from time to 

 time other benefices, he mainly resided. Living not far from 

 Kew he was the friend of the royalties, and although Horace 

 Walpole called him " a poor good primitive creature," he 

 was greatly admired and respected by them, and was a 

 close friend of Pope's, whose will, in fact, he witnessed. 



Sir Francis Darwin draws attention to the fact that 

 Hales' scientific work falls into two main classes : (1) physio- 

 logical and chemical, (2) inventions and suggestions on 

 matters connected with health and agriculture. It is with 

 the former we have mainly to deal. 



Hales, as we have pointed out, was the single successor 

 in the eighteenth century of Nehemiah Grew, but in his 

 time scientific men were less specialized than they are now, 

 and Hales was not only a leader in vegetable physiology, 



