"We shall finish our remarks on Sir Henry's work by making some observations upon a quotation made by Sir Henry Steuart from A Treatise on the Forming and Improving of Country Residences by the Author of the Encyclopaedia of Gardening etc.— an author who combines talent successful industry and enlightened benevolence in no common degree We are sorry to appear before this author whom we have long esteemed in opposition yet we regret the less as we consider him one of the few who prefer accuracy and truth to an old opinion and whose name stands too high to be affected by a casual misconception." (Matthew 1831, p. 295)As you can see, Matthew refers to the "Author of the Encyclopaedia of Gardening" rather than simply naming Loudon. This is quite strange, because Matthew was, otherwise, very outspoken and did not fear to openly criticise other scholars. In a previous post, I have already shown the further strange fact, that Matthew did not transport all the alterations that Steuart has taken the liberty to introduce into his quotation of Loudon. In some cases, Matthew reverted to the original usage of Loudon. This suggests that Matthew's re-quote was a dummy, and that Matthew did have Loudon's original at his disposal. He surely knew the Encyclopaedia of Gardening, for he chose to call Loudon "the Author" of that work rather than simply giving his name.
This strange evasiveness of the, otherwise, forthright Patrick Matthew suggests that he has lifted ideas from Loudon and did not want to credit that fact. By re-quoting Loudon via Steuart, he could pretend to not know the rest of Loudon's publications. Therefore, I searched the Encyclopaedia of Gardening for passages relevant to the idea of natural selection. Although Loudon's work has more to do with landscape design than natural history, the following passage indicates that the idea of competition and survival of the best adapted was already widely spread among scholars of that time (my emphasis):
" 6871. Sir W. Chambers and Price agree in recommending the imitation of natural forests in the arrangement of the species. In these nature disseminates her plants by scattering their seeds, and the offspring rise round the parent in masses or breadths, depending on a variety of circumstances, but chiefly on the facility which these seeds afford for being carried to a distance by the wind, the rain, and by birds or other animals. So disseminated they spring up, different sorts together, affected by various circumstances of soil and situation; and arrive at maturity, contending with other plants and trees, and with the browsing of animals. At last, that species which had enjoyed a maximum of natural advantages is found to prevail as far as this maximum extended, stretching along in masses and angular portions of surface, till circumstances changing in favor of some other species, that takes the prevalence in its turn. In this way it will generally be found, that the number of species, and the extent and style of the masses in which they prevail, bears a strict analogy to the changes of soil and surface; and this holds good, not only with respect to trees and shrubs, but to plants, grasses, and even the mossy tribe." Loudon (1824. "An Encyclopaedia of Gardening." London: Longman, Hurst, Rees, Brown and Green, p. 957)As already mentioned in my earlier post, Loudon also had a lot to say on the variety within species. The only thing still missing, here, was the idea of the transformation of species through the natural selection of varieties. That was a matter of simply putting the pieces of the puzzle together rather than of unmatched genius. We can conclude that Matthew has lifted the ideas of competition and natural selection from other sources and not thought them up himself. He did not cite the sources of the parts of the puzzle he solved. In this, his conduct met the same standards as that of other Victorian naturalists.
P.S.: The particular passage from Loudon quoted above sets us on a new search for the works of Sir W. Chambers and Price, because it could mean that they were not only recommending the imitation of natural forests, but also suggested natural selection and adaptation to circumstances as the reason for this recommendation.