314 ATKINSON— MORPHOLOGY AND [April 23. 



edulis Vitt./ as I have elsewhere suggested® (1900, 1901, 1903, p. 

 20). Excellent figures of this variety are given by Vittadini {I. c, 

 pi. 6) and by Bresadola'' (pi. 54). 



II. Origin of the Hymenophore Primoridum 



Primordimn of the Basidiocarp. — The primordia of the basi- 

 diocarps are elliptical or oval in outline, and reach a diameter of 

 3 mm. or 4 mm. before there is any internal evidence of a differentia- 

 tion of parts. The length is usually somewhat greater than the 

 transverse diameter. In specimens not so well nourished differentia- 

 tion may begin before the primordia have reached this size. The 

 primordium, from the size of 2 mm. to 4 mm. in diameter, consists 

 of a homogeneous interlacing of stout mycelial threads with rather 

 thick walls. In primordia 3 mm. to 4 mm. in diameter the hyphae 

 average about 5 /x to 7 ft in thickness, occasionally stouter ones are 

 seen which measure up to 10 /x. More slender threads are also inter- 

 mingled, but all sizes are so indiscriminately interwoven that no 

 structural differentiation is perceptible. In smaller primordia the 

 hyphae average less in diameter. In most of the primordia examined, 

 the sections are evenly stained throughout, but in a few a narrow 

 zone a short distance from the surface stains more deeply than the 

 external and internal tissue (Fig. 2). This suggested the possi- 

 bihty of a differentiation of an outer zone distinct from the bulk of 

 the fruit body, which is sometimes present in Agaricus campestris 

 and which I have called the protohlem}^ A similar zone is found in 

 some of the basidiocarps after the origin of the hymenophore funda- 

 ment, but in the material which I have examined it is the exception 

 rather than the rule, and I am inclined to the belief that it is due to 

 some condition which affects the rate of growth or increase of cer- 



■^ Vittadini, C, " Funghi Mangerecci," 44, 1835. 



8 Atkinson, Geo. F., " Studies of American Fungi ; Mushrooms, Edible, 

 Poisonous, etc.," 1st edition, I-VL, 1-275, 76 plates (223 figs.), Ithaca, N Y., 



1900. Idem, 2d edition, I-VL, 1-322, 86 plates (250 figs.), Ithaca, N. Y. 



1901. Idefn, New York City, 1903. 



9 Bresadola, G., " Funghi Mangerecci e Velenosi," 1899. 



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

 comtulus," Am. Jour. Bot., i, 3-22, pis. i, 2, 1914. "Homology of the Uni- 

 versal Veil in Agaricus," Myc. Centralb., 5, I3-I9> pls. 1-3, IQM- 



