LETTER XV. 



" Nothing seems more difficult than to see a thing as it really is, 

 imless it be the right interpretation of observed phenomena." 



Professor Owen. 



May 15, 1855. 



My Dear Sons, 



1. We have still to deal with other objections to 

 our theory of trees, and these perhaps more formidable 

 than any we have yet encountered. At least they are 

 advanced by one, who, in rank and authority as a 

 physiologist, stands second to none — I mean Dr 

 Carpenter. 



2, In his Principles of Physiology, General and 

 Comparative, this distinguished physiologist brings 

 under his review this theory of mine — as contained 

 in a paper which I published several years ago 

 in the Edinburgh New Philosophical Journal; and 

 he urges certain considerations which he regards 

 as fatal to it. The theory itself he states so well in 

 his own way that I cannot forbear here quoting his 



