Carpophore of some Agaricaceae . 687 
sections naturally correspond to a ring-shaped area in the entire carpophore, 
and they represent the primordium of the hymenium. Very soon after¬ 
wards the differentiation of a cup-shaped layer of deeply staining hyphae 
takes place, which extends upwards from the primordium of the hymenium 
over the summit of the carpophore, but always some distance below its sur¬ 
face (Fig. 14). This cup-shaped layer forms the primordium of the pileus. 
A little later a gill cavity is formed just below the hymenial primordium by 
the cessation in growth of the hyphae at that spot (Fig. 15). The gill cavity 
increases in size and the differentiation of the various parts of the fruit- 
body becomes more distinct (Fig. 16). The marginal veil, formed of neutral 
tissue present from the first , covers in the gill cavity. The universal veil, 
which is well developed over the summit of the young pileus, can only with 
difficulty be traced in the neighbourhood of the marginal veil as a distinct 
structure from this. The whole development of the hymenium and the 
formation of the gills takes place within the cavity which is curtained off 
from the exterior by the marginal veil (Fig. 17). 
Not until a late stage does the growth of the pileus rupture the mar¬ 
ginal veil along its margin and leave this structure as the * annulus ’ upon 
the stipe. The chief facts which result from my observations upon Armil¬ 
iaria mellea are that the primordium of the hymenium is the first part of 
the carpophore to be differentiated in this plant, and that this differentiation 
takes place endogenously. Fischer found that a palisade layer, marking off 
the pileus, was the first area to differentiate in Armiliaria mucida. It is 
not unlikely that there may be some variation in the exact spot in which 
the differentiation commences; in any case, my preparations of A. mellea 
show that the differentiation of the pileus follows rapidly upon that of the 
hymenium, and it is quite possible that under certain circumstances the 
differentiation of pileus and hymenium may be practically simultaneous, or 
that the c couche pileogene * may even be distinguished before the hymenium. 
On the other hand, however, the order of differentiation may be con¬ 
stantly distinct in the fruit-bodies of Armillaria mellea and A. mucida. 
Further observations can alone decide this. However this may be, the 
particular set of plants which I have examined correspond in this respect 
more closely with Atkinson’s observations upon Agaricns campestris , in 
which he found the primordium of the hymenium to be the first part to 
differentiate in the young carpophore. I am in complete agreement with 
both Atkinson and Fischer with regard to the endogenous origin of the 
hymenial primordium, and in finding the marginal veil to be present from 
the first and not formed as an aftergrowth as Hartig believed. 
In conclusion, I should like to express my thanks to the staff of the 
department of Cryptogamic Botany at the British Museum (Natural 
History) for their kind assistance in identifying the Fungi described above. 
z z 2 
