Homology of the “universal veil” in Agarzeus 15 
sporophore 6 ) of Agaricus arvensis are sliown in figs. 1—3. The first 
evidence of the internal annular gill cavity is sliown in fig. 1 and slightly 
later stages are presented in figs. 2 and 3. The primordium of the 
hymenophore lies just above the gill cavity, and is differentiated by the 
darker color of the tissue in figs. 2 and 3. The hymenophore is there- 
fore not only endogenous in origin, but originates deep witliin the fruit 
body. The primordium of the pileus margin lies just above the outer 
angle of the gill cavity and is merged with the hymenophore primordium 
at this early stage. External to this is a broad zone of looser tissue 
with thick walled hyphae which envelops the young fruit body, Fig. 8 is 
a more highly magnified photomicrograpk showing the very young prim¬ 
ordium of the pileus margin at the junction of lines perpendicular to a, a. 
The general course of the hyphae is outward and downward. The loose 
meslied tissue below is the first evidence of the gill cavity, the threads 
lagging behind in growth are torn appart. The hyphae in the gill cavity 
and tliose of the hymenophore and pileus primordium are thin walled. 
The loose meslied tissue at the right of the pileus margin in the 
same figure (fig. 8) belongs to the external zone which envelops the 
entire fruit body at this and somewhat later stages. The thick walled 
hyphae of this zone are readily distinguished from the thinner walled 
more compact ones of the pileus and hymenophore primordia, and from 
tliose of the loose meshed tissue below the hymenophore which is sepa- 
rating to form the gill cavity. In fig. 9 an older stage is represented, a 
more highly magnified illustration of a portion of fig. 3. The margin of 
the pileus here is at the junction of lines perpendicular from b, b. 
Comparison with Agaricus comtulus. 
A similar zone of loose-meshed tissue of thick walled hyphae for- 
ming an enveloping zone around the pileus and stem fundaments is 
present in Agaricus comtulus and sliown in fig. 7. The hymenophore 
primordium here appears as two symmetrically disposed dark areas in 
the longitudinal section, the dark area between them and forming a 
convex area witliin the upper part of the sporophore is the pileus prim¬ 
ordium. The dark area below which broadens downward is the stem 
fundament. 
Union of the pileus and the external zone. 
Older stages of this external zone of loose meshed tissue, with thick 
walled hyphae, are sliown in figs. 5, 6 and 10. The elements of the 
pileus primordium become more active from the margin upward toward 
the center and extending outward (the hyphae, toward the margin being 
more strongly epinastic) grow into the inner portion of this external 
zone, binding it to the surface of the pileus. 
6) In my article: The development of Agaricus arvensis and A. 
comtulus Am. Journ. Bot. 1, 3—22; pls. 1, 2, 1914 I used in several places the 
term “carpophore”, for the fruit body. Garnsey and BalfoüR, in the English 
Edition of de Bary’s Comparative morphology and biology of the Fungi, 
Mycetozoa and Bacteria, Oxford 1887 define carpophore (p. 493) as a ”stalk 
of a sporocarp”. It is perhaps, therefore not an apt term for the fruit body (Frucht- 
körper), or basidiocarp of the basidiomycetes. 
