From H. C. Watson   20 June 1856

My dear Sir

The title page of my ‘Remarks on Geogr. Distr. Brit. Plts.’ bears the date of 1835. The published data towards compiling such a List as that termed ‘Geog^l. Extension’ have been greatly increased & corrected in the past score years. So that many gaps in the List would now be filled, & sundry corrections should be made.¹ Still, the general fact remains as there imperfectly appearing, that plants common to Europe & America range far northward, in one or both, with few exceptions.²

Since giving my own reply I communicated your two queries to Mr. J. T. Syme, a good European botanist, & asked his opinion.³ He writes:—

l^st. “I quite agree with you that plants of cultivated ground do not vary more than others of the same genus, growing in other situations”.

2^d. “I agree with you that very few European species are wild in U.S. except such as pass 55^o.”

Mr S. illustrates the first of these two opinions, by naming several agrestal species⁴ which do not vary so much as allied species which grow in other situations than tilled ground.

In illustrating the second, he gives a list of 22 species, noted in running thro’ Gray’s Botany of the N. States,⁵ which he thinks may not pass much north of 55 in Europe. i.e. “which do not occur in Scandinavia, or beyond 55 in Britain.”

The paucity of this list is the essential point; & even in this short list of 22, some 5 or 6 may likely have passed by human agency from Europe to America, or vice versa. Two are common to America & the British Isles, without reaching European continent. Two are common to Europe & E. America, but not British. Three connect with America better by way of E. Asia & W. America, than by way of W. Europe & E. America. Two are littoral plants. Four are natant aquatics; & such plants are often difficult to discriminate specifically, & are widely diffused either in seeming or really.

I am not prepared to say whether the number of species common to E. Asia & W. America is less or more than of those common to W. Europe & E. America. I doubt whether the botany of E. Asia & W. America is sufficiently known to allow of a true comparison.— Under existing knowledge, the list for W. Europe & E. America would proby. be the more numerous.

Truly I cannot at all say whether the Americo-European species, as a prevailing rule, could have spread from one Continent to the other by way of Kamchatka & Aleoutia, with some moderate changes of the land. Perhaps there are too many of these plants not yet known on the two coasts of the upper part of the N. Pacific, & intervening islands, to allow of the hypothesis, that they did so spread.

As to the Hispano-Hibernians. These are few, & you are aware chiefly Heaths & Saxifrages. Unite Ireland, England, & France, & project a few promontories into the Oceanic Bay thus formed, or throw up some few Volcanic cones between Spain & Ireland,—breakwaters to be gradually washed away again,—& you would make the physical conditions by which those Heaths & Saxifrages might pass from Ireland to Spain, or from Spain to Ireland. The Hispano-Hibernian Heaths (Arbutus Unedo, Menziesia polifolia, Erica Mediterranea, ciliaris, Mackaiana) are less patient of cold than the Saxifrages. I suppose all are “semi-alpine” in the latitude of Spain; the Saxifrages are so in that of Ireland. And if the latter naturalize themselves in Britain, it is in the Dales of Yorkshire, about the Lakes of Engl^d., or the borders of the Highlands. Whether they could exist on a coast cold enough to admit of Glaciers, seems doubtful & scarcely probable.—

Sorry I can give no better answers or comments on your queries.— I suspect they must be passed down to a future generation for solution—

Very truly | Hewett C. Watson