684 Beer.—Notes on the Development of the 
no additions were made to our knowledge of the development of the fruit- 
bodies of these Fungi. In 1906, however, the long silence was broken, and 
Professor G. F. Atkinson ( 5 ) published an admirable account of the develop¬ 
ment of the carpophore of the mushroom. 
He found that the young homogeneous fruit-body, in its earliest stage, 
shows no differentiation into parts (except the rudimentary universal veil), 
and is to be considered as the primordium of the carpophore. The first 
differentiation consists in the appearance of a ring of deeply staining hyphae 
near the upper end of the young fruit-body and some distance below the 
surface. This is the primordium of the hymenium, and it marks the 
differentiation of the primordium of the fruit-body into the primordium of 
the pileus and that of the stem and marginal veil, the latter being the 
tissue of the young fruit-body external to the hymenial primordium and 
continuous with what is to be the margin of the pileus above and with the 
undifferentiated stem surface below. 
Soon after the hymenial primordium has been formed the tissue of the 
pileus primordium becomes definitely organized, and appears as a deeply 
staining area lying some depth below the surface. 
The three salient facts which Professor Atkinson demonstrated in 
Agaricus campestris were :— 
1. The hymenial primordium was the first structure to become 
differentiated in the homogeneous fruit-body. 
2. This hymenial primordium arises endogenously and the marginal 
veil is not an aftergrowth. 
3. The tissue of the pileus (the ‘ couche pileogene’ of F'ayod) arises in 
this plant after the appearance of the hymenial ring. 
A few years later C. C. E. Fischer (6) published an account of his study 
of the development of the carpophore of Armillaria mucida. He finds that 
this does not at all agree with the description given by Robert Hartig in 
the case of A. mellea. 
No open furrow is formed round the young fruit-body which subse¬ 
quently becomes closed by the aftergrowth of a marginal veil. On the 
contrary, Fischer finds the development of this plant to resemble that of 
the mushroom, as given by Atkinson, in so far as, in both species, the 
hymenium originates endogenously and is separated from the exterior 
from the first by a layer of neutral tissue which constitutes the marginal 
veil. 
If I read his account correctly, however, Armillaria mucida differs 
from Agaricus campestris in that in the former plant the pileus (‘ couche 
pileogene ’ of F'ayod) precedes the appearance of the hymenial rudiment. 
Fischer states that the hyphae near the apex of the young fruit-body 
show a tendency to radiate towards the periphery and form a subcuticular 
palisade layer of tissue. This palisade layer defines the rudiment of the 
