Mr. George B. Emerson, in his valuable work on the "Trees and Shrubs of Massachusetts," suggests as a cause (undoubtedly the true one) for the dying out of old forests, "the exhaustion of the nutritious elements of the soil required for their vigorous and successful growth." But he is evidently at fault in his speculations as to the alternations of forest growths. The Cretan labyrinth that everywhere confronts him is the "seed-theory," which is so inextricable to him that he constantly stumbles, as one scientifically blind, yet eager to lead the blind. All the phenomenal facts with which he deals admirably fit into the Bible genesis, but he fails to see it because the sublime truth (with him) lies locked up in an unmeaning translation. He is indefatigable, however, in his hunt after seeds where there are no seeds, and in his jumps at conclusions where there are manifestly no data to justify them. He says: "Nature points out in various ways, and the observation of practical men has almost uniformly confirmed the conclusion to which the philosophical botanist has come from theoretical considerations, that a rotation of crops is as important in the forests as in the cultivated fields." And he supplements this statement (measurably a true one) by adding that "a pine forest is often, without the agency of man, succeeded by an oak forest, _where there were a few oaks previously scattered through the woods to furnish seed._" This is a very cautious, as well as circumspect, statement; but one that Mr. Emerson would not have made, had his experience and observation been that of Professor Agassiz, Professor Marsh, and others we might name. His few oaks previously scattered through the woods are no doubt among the "theoretical considerations" taken into account by him, as a philosophical botanist rather than a practical one. They were necessary for the extreme caution with which he would state a proposition when its "conditioning facts" were not fully known by him. His anxiety to account for the appearance of an oak forest in the place of a pine, where the latter had been cut off, was commendable enough to justify him in a pretty broad supposition, but not in any such general statement as he here makes. Had he consulted any of the older inhabitants of Westford, Littleton, and adjoining towns, in his own state, he would have found that not a few oak forests had succeeded the pine without the intervention of "scattered oaks," or even scattered acorns, in the localities named. Nor would his "squirrel-theory" of distribution have been very confidently adhered to, fifty years ago, in localties where the shagbark walnut was almost as abundant as the white oak itself. No squirrel will gather acorns where he can possibly get hickory nuts, and few will gather hickory nuts where the larger and thinner-shelled walnuts are to be had for the picking. The squirrel is provident, but no more so than he is fastidious in the choice of his food. He never plants acorns