The development of Armillaria mellea 
117 
outward toward the surface. This central zone is stained very faintly and 
the cell walls are thin. But scattered through it are slender, flexuous, 
curved, hyphae, which pursue a winding course, are 3—4 // in diameter, 
rich in protoplasm and deeply stained. 
A slightly older stage is shown in figs. 2—4, the young carpophore 
measuring 0,75 mm in diameter. The radiating hyphae are longer, mea¬ 
suring up to 150 /a while in still older carpophores they reach 200—300//. 
This carpophore is interesting since it shows the very earliest primordium 
of the hymenophore. Just above a in figs. 2 and 4 are seen five or six 
slender, curved hyphae growing in a downward direction. On the opposite 
side is seen another group of similar hyphae. One of these groups is 
just exterior to a minute puncture in the fruit body, which of course must 
not be taken for the gill cavity. The hyphae constituting the first ele¬ 
ments of the primordium of the hymenophore appear to be of the same 
character as the delicate hyphae rich in protoplasm scattered through the 
central zone of the fruit body described above. The direction of the 
hyphae forming the hymepophore primordium indicates that epinastic 
growth has entered in an annular region of the fruit body at this point. 
It will be observed that the radial hyphae of the outer layer of the “uni¬ 
versal veil”, in an annular zone at this point, are affected by this epinastic 
condition, and are bent in a decidedly downward direction. Were it not 
for the fact that in younger fruit bodies, as shown in fig. 1, the hyphae 
of this outer layer are all radial, the condition represented in figs. 2—4 
might be taken to justify Hartig’s theory of a downward growth of 
hyphae from the margin of young pileus to cover the hymenophore pri¬ 
mordium. This is a good illustration of the difficulty of determining the 
exact order of events in Armillaria mellea if the stages at the time of, 
and immediately following, the differentiation of the hymenophore pri¬ 
mordium, are the only ones considered, since this zone of radial hyphae 
of the “universal veil” is rather loose and there is only a slight develop¬ 
ment of the “cortex” at this point. The hyphae are quickly drawn into 
a direction suggesting downward and upward growth forming a thin and 
loose veil. The condition is very different in the enveloping layers of 
radial hyphae and cortex in Lepiota clypeolaria (described elsewhere) 
since the epinastic influence does not extend to these layers but is con¬ 
fined to the margin of the pileus primordium. But the condition found 
in the very young carpophores as shown in figs. 2—4 indicates clearly 
when compared with the condition shown in fig. 1, that, the primordium 
of the hymenophore is of endogenous origin in Armillaria mellea, and 
that the radial hyphae in the annular zone exterior to the hymenophore 
primordium, have not grown in a downward direction, but are later bent 
downward as the result of epinasty of the tissue in this region. Further¬ 
more no annular external furrow is as yet visible over which the hyphae 
were said by Hartig to grow, though the epinasty of the hyphae at this 
point suggest at first, when seen under the microscope, a superficial 
annular furrow. 
Later stages of fruit bodies 1 to 1,5 mm in diameter show the 
primordium of the hymenophore well differentiated, often with the annular 
gill cavity formed, though in some cases the loose textured tissue of the 
marginal veil completely fills the area between the hymenophore and 
stipe for some time. With the growth of the carpophore, intercalary 
