52 INVOLUTION [Chap. II 



Letter 19 every plant must be occasionally crossed. I find, however, 

 plenty of difficulty in showing even a vague probability of 

 this ; especially in the Leguminosae, though their [structure ? ] 

 is inimitably adapted to favour crossing, I have never yet 

 met with but one instance of a natural mongrel (nor mule ?) in 

 this family. 



I shall be particularly curious to hear some account of the 

 appearance and origin of the Ayrshire Irish Yew. And now 

 for the main object of my letter : it is to ask whether you 

 would just run your eye over the proof of my Galapagos 

 chapter, 1 where I mention the plants, to see that I have made 

 no blunders, or spelt any of the scientific names wrongly. As 

 I daresay you will so far oblige me, will you let me know 

 a few days before, when you leave Edinburgh and how 

 long you stay at Kinnordy, so that my letter might catch 

 you. I am not surprised at my collection from James 

 Island differing from others, as the damp upland district 

 (where I slept two nights) is six miles from the coast, and 

 no naturalist except myself probably ever ascended to it. 

 Cuming had never even heard of it. Cuming tells me that he 

 was on Charles, James, and Albemarle Islands, and that he 

 cannot remember from my description the Scalesia, but thinks 

 he could if he saw a specimen. I have no idea of the origin of 

 the distribution of the Galapagos shells, about which you ask. 

 I presume (after Forbes' excellent remarks on the facilities 

 by which embryo-shells are transported) that the Pacific shells 

 have been borne thither by currents ; but the currents all run 

 the other way. 



Letter 20 Edward Forbes 2 to C. Darwin. 



Edward Forbes was at work on his celebrated paper in the Geological 

 Survey Memoirs for 1846. We have not seen the letter of Darwin's to 

 which this is a reply, nor, indeed, any of his letters to Forbes. The 



1 In the second edition of the Naturalist's Voyage. 



- Edward Forbes, F.R.S. (1815 — 1854), filled the office of Palaeon- 

 tologist to the Ordnance Geological Survey, and afterwards became 

 President of the Geological Society; in 1854 — the last year of his life — 

 he was appointed to the Chair of Natural History in the University of 

 Edinburgh. Forbes published many papers on geological, zoological, 

 and botanical subjects, one of his most remarkable contributions being 

 the well-known essay "On the Connexion between the Distribution of 



