54 DIVISION 1.—GENERAL MORPHOLOGY. 
like the spokes of a wheel. They are closely interwoven at the centre, but separated 
towards the circumference by constantly increasing interspaces, and thus the surface 
is covered with spreading hairs. These appear under the microscope to be colourless 
or of a uniform brownish colour, while the hyphae of the central tissue is coloured by 
granules of a reddish-yellow pigment. As the development proceeds the lower half 
of the hemispherical body, lower that is in relation to the substratum which is 
supposed to be vertical, takes a reddish-yellow tint and its surface becomes smooth 
and velvety. Thin radial sections following the direction of the hyphae show that, 
as far as the last-mentioned character extends, numerous hyphae, most of which 
contain reddish-yellow pigment-granules, have grown from the central weft to 
the surface and have thrust themselves in large numbers everywhere between 
the previously formed hairs and enclosed them. The upper half of the hemispherical 
compound sporophore retains its original character. Now begins a vigorous longi- 
tudinal and apical growth of the hyphae which run into the margin of the reddish- 
yellow under surface of the young pileus, while those which terminate in its middle 
portions elongate but little or not at all. Hence the upper surface becomes concave 
and the horizontal portion of the pileus raises itself from the substratum, 
while the growth of the hyphae advances at its margin. Sections show that 
the margin consists of a massive and compact layer of truncated rather thick 
hyphal extremities, which incline slightly towards the under surface and usually contain 
reddish-yellow pigment-granules. These extremities join on to the perfect hyphae of the 
pileus close to the point of origin of the latter ; these perfect hyphae being distinguished 
from them by their pellucid contents, but not by greater thickness, and running in 
radiating lines parallel to the surface of the pileus. The differentiation of the tissue 
of the pileus begins close behind the advancing margin, and results in a lower colourless 
medullary stratum, and an upper thin rind-stratum distinguished by membranes 
of a clear brown colour. Numerous hairs begin to be developed on the upper surface 
nearer the margin, and the hymenium on the lower surface. The former are simple 
stout hyphal branches which either spread or are curved backwards; the outermost 
of them project beyond and mostly cover the growing margin. Numerous branches 
run obliquely and with a slight curve close behind the margin towards the hymenial 
surface. The nearer the base of the pileus, the more numerous are the hymenial 
elements which are introduced between those previously formed, and the more 
decidedly do they assume the vertical position as regards the surface of the original 
constituents of the hymenium. The portion of the pileus which is attached to the 
substratum shows essentially the same mode of growth as that which projects from 
it, only the hairs on its outer surface penetrate as rhizoids into the substratum. 
Measurements by J. Schmitz and microscopic examination show that the enlargement 
of the pileus takes place only next the margin’. 
4. The unveiled umbrella-shaped pileus with central stalk of the Agariei (Fig. 24) 
appears at first on the mycelium as a small cylindrical, ovoid, or even spherical body, 
pointed at the upper end and consisting throughout of very delicate firmly united 
hyphae running’ longitudinally. At a very early stage, when the entire structure 
in the specimens which I have examined is 3-2 mm. in length, the extremities of 
the hyphae at the upper end spread in every direction as they grow and at the same 
time branch copiously. This gives rise to a small hemispherical head separated 
from the lower portion by a shallow annular furrow, the primordium of the pileus 
(Fig. 24a). A vigorous growth then commences in the extremities of the hyphae 
which form its margin, and they constantly elongate, but at the same time retain 
their original thickness, and continue as closely woven together as at first ; there 
must therefore be a constant introduction of new branches between the earlier 
ones in the direction of the surface of the pileus. The hyphae which run towards 

1 See also R. Hartig, Zersetzungserscheinungen d. Holzes, p. 130, t. XVIII. 
