324 ATKINSON— MORPHOLOGY AND [April 23, 



broad, and the surface slopes outward at a strong angle. The sur- 

 face outline of the stem is quite clearly differentiated from the 

 loose ground tissue forming the marginal veil, because of the deeper 

 staining property of the stem shown in longitudinal sections (Fig. 

 32). Its differentiation and organization agrees entirely with that 

 described for Agaricus canipestris,-^ Agaricus arvensis and A. 

 comtulusP 



Organization of the Marginal Veil. — The organization and limits 

 of the marginal veil, or partial veil, as it is sometimes called, in 

 Agaricus arvensis, A. conitulus and A. campestris, has been very 

 fully discussed in previous papers-^ (13-15, 1914), briefly in an- 

 other^'^ (17, 1914). Its organization and composition in Agaricus 

 rodmani is in the main similar, its different features being due to 

 its more robust character, the stouter pileus and shorter stem. 

 The fundament of the marginal veil is ground tissue in the angle 

 between the primordial hymenophore zone and the stem fundament, 

 including on its outer surface a narrow section of the blematogen 

 layer. The ground tissue in this angle is indicated in VP (veil 

 primordium) in diagram 3, and the corresponding areas in Figs. 3, 

 5, 7, 9-14 can readily be understood. There is considerable increase 

 in this ground tissue by growth of the portion clothing the stem 

 fundament. It is also added to by growth of the hyph« at the 

 margin of the pileus. The mass of the loose inner surface is often 

 crowded up against the edges of the gills by the involute margin 01 

 the pileus pushing it upward, due to epinastic growth. 



In such robust specimens usually presented by Agaricus rodmani 

 the blematogen layer is comparatively thick but still forms a com- 

 paratively small portion of the marginal veil, and lies on the outer 

 under surface of the lower limb of the annulus. By the incurving 

 of the thick margin of the pileus its edge is crowded into the thick 

 veil, and presses against the stem, thus separating the veil, which 

 later becomes the annulus, into an tipper and lower limb. As stated 

 above, the fact that the short stem elongates but little in comparison 



28 Atkinson, Geo. F., "The Development of Agaricus campestris," Bot. 

 Gas., 42: 241-264, pis. 7-12, igo6. 



29 Atkinson, Geo. F., " The Development of Agaricus arvensis and A. 

 comtulus," Am. Jour. Bot., i. 3-22 pis. i, 2, 1914. 



30 Atkinson, Geo. F., " Homology of the Universal Veil in Agaricus, 

 Myc. Cantralb., 5, 13-19, pis. 1-13, 1914. 



