And hardly anybody will believe me when I declare it an introduced plant.

I daresay it is equally abundant in Spain.

I doubt if it is more so.
Engelmann and I have been noting the species truly indigenous here which, becoming ruderal or campestral, are increasing in the number of individuals instead of diminishing as the country becomes more settled and forests removed.

The list of our wild plants which have become true weeds is larger than I had supposed, and these have probably all of them increased their geographical range--at least, have multiplied in numbers in the Northern States since settlements.
Some time ago I sent a copy of the first part of my little essay on the statistics (330/1.

"Statistics of the Flora of the Northern U.S." ("Silliman's Journal," XXII.