The plants of the division Hypogaei or Hymenogastreae are subterranean in habit, preferring a sandy soil. They are usually somewhat globose in form, having a thick outer coat or peridium, though in some of the genera the outer coat is very thin or obsolete. They are dingy in color. In the young plants the interior substance somewhat resembles that of the truffle, but is streaked and mottled. When old the gleba consists of a dusty mass of threads and spores. They are known under various appellations, such as "underground puff-balls," "false truffles," etc. The Hypogaei are analogous to the Tuberacei, except that the spores are not contained in asci as in the latter. Cooke says they appear to be the link which unites the Basidiomycetes to the Ascomycetes by means of the Tuberacei or genuine Truffles. In the young stage the basidia in the Hypogaei are easily distinguished by the aid of the microscope. In external features and habit of growth the species of Elaphomyces, a genus of Tuberacei, closely resemble the Hypogaei, and in old age, when the _asci_ have disappeared, it is difficult to distinguish the plants of this genus from the Hypogaei. The genus _Melanogaster_ contains an edible species, _M. variegatus_, Tulasne, commonly known in Europe as the "Red Truffle" or "False Truffle." _M. variegatus_ is usually gregarious and subterranean in habit. The exterior is minutely granular, tawny yellow or reddish rust color; the interior soft, bluish-black, streaked with yellow, the spore mass in maturity becoming pubescent. The odor is pleasantly aromatic, and the taste sweet. Under trees in woods. The variety _Broomeianus_ Berk. is paler in the marbling, which shows reddish instead of yellow streaks. The pulpy mass is at first white, changing to a yellowish, smoky hue. LYCOPERDACEAE AND PHALLOIDEAE. The plants figured in Plates G and H belong to the Lycoperdaceae and Phalloideae. LYCOPERDACEAE. Massee, who has given the Puff-Ball group very close study, says that in the gleba of the Lycoperdaceae, "at a very early period two sets of hyphae are present. One, thin-walled, colorless, septate and rich in protoplasm, gives origin to the trama, and elements of the hymenium, and usually disappears entirely after the formation of the spores; the second type consists of long thick-walled aseptate or sparsely septate, often colored hyphae, which are persistent and form the capillitium. The latter are branches of the hyphae forming the hymenium." GENERA LYCOPERDON AND BOVISTA. To the genera Lycoperdon and Bovista belong most of the "Puff-balls" and all of the species figured in Plate G. In the plants of these two genera the peridium is more or less distinctly double, and the hyphae, or delicate threads which are seen mixed with the dusty mass of spores in the mature plant, forming what is called the capillitium, are an important element in classification.