Besides these two most valuable species, our forests produce the Pignut hickory (C. porcina), a lofty tree with five to seven pairs of leaflets, so called from the comparative worthlessness of its fruit; which is very thick-shelled, and generally is left on the ground for the swine, squirrels, etc., to devour. It is easily distinguished in winter by the smaller size of its brown shoots, and its small oval buds. Its wood is considered the toughest and strongest of any of the trees of this section. The thick Shellbark hickory (C. laciniosa) resembles much in size and appearance the common Shellbark; but the nuts are double the size, the shell much thicker and yellowish, while that of the latter is white. It is but little known except west of the Alleghanies. The Mockernut hickory (C. tomentosa) is so called from the deceptive appearance of the nuts, which are generally of large size, but contain only a very small kernel. The leaves are composed of but four pairs of sessile leaflets, with an odd one at the end. The trunk of the old trees is very rugged, and the wood is one of the best for fuel.