1915-] DEVELOPMENT OF AGARICUS RODMANI. 319 



the hyph^e in the young hymenophore, crowding in between the 

 older ones, as well as their increase in diameter, produces a great 

 pressure in this region. As a result of this increasing pressure 

 within the arch a strong tension is exerted on the ground tissue 

 below and adjacent to the arch. The ground tissue at this point 

 is thus torn apart, forming a distinct opening, or cavity, beneath 

 the young hymenophore, which is known as the annular gill cavity. 

 The continuity as a general, annular, internal cavity can easily be 

 determined by serial longitudinal sections through the young fruit 

 body, the sections being made as indicated in diagrams 3 and 4, the 

 knife travelling through the basidiocarp in the direction indicated 

 by the Hues i, 2, 3. As the knife passes the region marked by the 

 line I, the sections will show a single cavity elongated transversely 

 as shown in Figs. 6 and 8, 15 and 16. As the knife passes into the 

 stem area the sections will show two cavities situated symmetrically 

 as in Figs. 5 and 7 (or as in diagrams 3 and 4). Then as the knife 

 passes out of the stem area, into the region indicated by the line 3, 

 the sections will again show a single cavity elongated transversely. 

 The annular gill cavity^^ varies in strength in different indi- 

 viduals and at different stages of development. Sometimes it is 

 very weak, at other times it is quite strong. The tearing apart of 

 the ground tissue often leaves it with quite an open mesh, and the 

 surface next the gill cavity is more or less frazzled. The gill cavity 

 is stronger next the stem where the hymenophore is older, and is 

 weaker toward the margin. Where the cavity is weak, isolated 

 threads or irregular strands of the ground tissue are not completely 

 torn away from the hymenophore, and the cavity is thus often tra- 

 versed by lagging elements of the ground tissue. At a later stage, 

 after the origin of the lamellae, the annular cavity in some indi- 



12 In a recent paper, after describing the gills in Coprinus micaceus, 

 Levine (" The Origin and Development of the Lamellae in Coprinus micaceus" 

 Am. Jour. Bot., i, 343-356, pis. 39, 40, 1914), makes the statement (p. 352) 

 that " There is no general gill cavity as described by Hoffmann, deBary, 

 Atkinson, and others." Since deBary (" Morphologie und Physiologic der 

 Pilze, Flechten und Myxomyceten," 69, 1866) is the only person hitherto who 

 has announced the presence of a general annular gill cavity in Coprinus 

 micaceus, this statement by Levine can only be interpreted as a general 

 denial of the presence of a general annular gill cavity in the species in vi^hich 

 it has thus far been described, a rather rash statement which will be re- 

 ferred to again in the discussion of the origin of the lamellae. 



