3S HEROES OF SCIENCE. 



not more than two years old. The hard heart- 

 wood does not convey sap, but in some trees, Hke 

 the poplar, sap moves in the very centre. 



The elaborated sap returns from the leaves in a 

 slow stream, through the delicate cellular structures 

 of the bark, right down to the root, giving rise to 

 the cambium layer, from the inner surface of which 

 the annual layer of young wood is formed. 



At this time Ray began to prepare for the press 

 his " CpMeetiojj^f Proverbs," a curious book in its 

 way, by which he is perhaps better known to the 

 generality of his countrymen, than by any other of 

 his literary labours. 



The first edition was published in 1672, but the 

 work was subsequently much enlarged, and the 

 author may almost be said to have exhausted his 

 subject. From its very nature, delicacy and refine- 

 ment had often to be dispensed with, but this is 

 evidently not the fault or the aim of the writer. 

 His learning and critical acuteness diffuse light 

 over the whole, and make us overlook the coarse 

 vehicle of our instruction. The first edition of the 

 " Catalogue of English Plants," already mentioned, 

 came out in 1670, and the second in 1677. Their 

 great author gave his work to the world with that 

 diffidence for which he alone, perhaps, could per- 

 ceive any just foundation. It was a wonderful 

 book, considering that there was no recognized 

 authority to help the author, who, seeing that there 

 must be some real method in nature, strove to 

 arrange or classify plants by the similarity or 



