In Pleurotus the stem is lateral or absent. The plants are epiphytal, usually springing from the decaying bark of trees and old stumps. In Clitocybe the plants are characterized by a deeply depressed, often narrow cap, with the gills acutely adnate, or running far down the stem, which is elastic, with a fibrous outer coat covered with minute fibers. Many of the species have a fragrant odor. The Tricholomas are stout and fleshy, somewhat resembling the Russulas, but distinguished from them by the sinuate character of the gills, which show a slight notched or toothed depression just before reaching the stem (represented in Fig. 4, Plate IV). Typical species of Armillaria show a well-defined ring and scales upon the stem, the remains of the partial veil, and the plants are usually large, and caespitose. The Lepiotas are recognized by the soft, thready character of the fleshy portion of the cap, and the fringed scales formed by the breaking of the cuticle. The ease with which the ringed stem is removed from its socket in the cap is another characteristic which distinguishes the plants from those of other genera. The Amanitas are distinguished by the volva, which sheathes the somewhat bulbous stem at its base and the ring and veil which in the young plant are very distinct features, the whole plant in embryo being enveloped in the volva. The Amanita group, besides containing some very good edible species, is also credited with containing the most dangerous species of all the mushroom family, and some which are undoubtedly fatal in their effects.[A] [A] A more detailed description of this group will appear in No. 5 of this series. The Nyctali are minute mushrooms parasitic on other mushrooms. In Omphalia, the plants are quite small, with membranaceous caps, gills truly decurrent, and cartilaginous stems. The Myceneae are generally very small, slender, and fragile, usually caespitose, with bell-shaped caps, sinuate gills, not decurrent, and cartilaginous stems. In some species the plants exude a milky juice. In the genera Panus, Lentinus, Lenzites, Schizophyllum, Xerotus, and Trogia, the plants are leathery or coriaceous, dry and tough, and though none are recorded as poisonous, they are too tough to be edible. The mushrooms having pink or salmon colored spores, section Rhodosporii, form the smallest of the four primary groups of Agaricini, the number of known species not exceeding 400, and most of these are tasteless, or of disagreeable odor, while some are recorded as unwholesome. The species are pink-gilled when mature, though often white or whitish when very young.