W. S. Coleman, British Butterflies: Figures and Descriptions of Every Native Species
“ Many a young botanist would be puzzled at first sight to tell a sloe-bush from a buckthorn-bush. Not so, however, with our Brimstone butterfly: passing by all the juicy hedge-plants, which look quite as suitable, one would think, she, with botanical acumen, fixes upon the buckthorn; either the common one, or, if that is not at hand, upon another species of rhamnus—the berry-bearing alder—which, though a very different looking plant, is of the same genus, and shares the same properties. ”
