Fig. 6. Sporangium, x 30. Fig. 6 _a_. A part of the peridial wall, seen from within, x 84. _Ceratiomyxa fruticulosa_ (Muell.) Macbr., p. 19. Fig. 7. Three sporiferous pillars, x about 40. Fig. 7 _a_. Tip of a single pillar, x 84. _Hemitrichia stipata_ (Schw.) Macbr., p. 262. Fig. 8. Sporangia, x 6. Fig. 8 _a_. The capillitium of the same species, x 750. Fig. 8 _b_. A single spore, x 1000. [Illustration: PLATE I] EXPLANATION OF PLATE II _Perichaena corticalis_ (Batsch) Rost., p. 243. Fig. 1. Sporangia, x 10. Fig. 1 _a_. A single spore, as if in section, x 900. Fig. 1 _b_. The capillitial thread, x 750. _Lachnobolus occidentalis_ Macbr., p. 246. Fig. 2. The sporangia, x 8. Fig. 2 _a_. A portion of the capillitium, x 750. Fig. 2 _b_. Spores, x 750. See also 4 and 4 a below. _Arcyria cinerea_ (Bull.) Pers., p. 254. Fig. 3. The expanded fructifications, x 5. Fig. 3 _a_. Tip of a single capillitium mass, x 40. _Lachnobolus occidentalis_ Macbr., p. 246. Fig. 4. A cluster of sporangia, x 3; cylindric type. Fig. 4 _a_. Capillitium, x 750; to show characteristic surface of the threads. _Arcyria denudata_ (Linn.) Pers., p. 253. Fig. 5. Sporangia, two expanded, one still closed, x 20. Fig. 5 _a_. A part of the capillitium of the same species, x 750. _Arcyria nutans_ (Bull.) Grev., p. 249. Fig. 6. Expanded capillitium, etc., x 10. Fig. 6 _a_. Capillitium, x 750. Fig. 6 _b_. A piece of the capillitium thread, x 1400. _Ophiotheca wrightii_ Berk. & C., p. 241. Fig. 7. A single sporangium, x 8. Fig. 7 _a_. A node of the capillitial thread, x 750. Fig. 7 _b_. A spore, x 750. _Oligonema nitens_ (Lib.) Rost., p. 280. Fig. 8. A single elater, x 750. Figs. 8 _a_ and 8 _b_. Spores, x 1000. _Badhamia macrocarpa_ Rost., p. 37. Var. _gracilis_. Fig. 9. Two sporangia, x 600. [Illustration: PLATE II] EXPLANATION OF PLATE III _Hemitrichia clavata_ (Pers.) Rost., p. 264. Fig. 1. Three sporangia, one closed, x 8. Fig. 1 _b_. A single spore, x 1400. _Hemitrichia vesparium_ (Batsch) Macbr., p. 262. Fig. 2. Tip of the elater of capillitial thread, x 1400. Fig. 2 _a_. A single spore, x 1400. _Trichia iowensis_ Macbr., p. 269. Fig. 3. A cluster of sporangia, x 5. Fig. 3 _a_. Tip of a branching elater, x 750. Fig. 3 _b_. A single spore, x 750. See also Plate X., Fig. 5. _Hemitrichia serpula_ Scop., p. 260. Fig. 4. A plasmodiocarp, x 3. Fig. 4 _a_. A single spore, x 1400. Fig. 4 _b_. An elater-tip, x 1400. _Trichia inconspicua_ Rost., p. 268. Fig. 5. A cluster of sporangia, x 12. Fig. 5 _a_. Tip of an elater, x 1400. Fig. 5 _b_. A single spore, x 750. _Physarum oblatum_ Macbr., p. 91. Fig. 6. A single sporangium, x 20; stipe shown of unusual length. Fig. 6 _a_. A single spore, x 1000. See also Plate XIV., Fig. 3. _Physarum auriscalpium_ (Cke.) Lister, p. 90. Fig. 7. A single sporangium, x 20; a New York specimen. Fig. 7 _a_. A single spore, x 1000. _Arcyria nodulosa_ Macbr., p. 252.