32 DIVISION I.—GENERAL MORPHOLOGY. 
to be spikey ; it often appears along the veins of the leaf, but always outside the 
wood-bundles. I found the sclerotia of P. Candolleana on oak-leaves, but there also 
only in the parenchyma. But the sclerotium of a small Peziza which inhabits the 
leaves of Prunus insinuates itself among all the elements of the veins of the leaf. 
d. The structure of the sclerotia of several of the Hymenomycetes, especially Agaricus 
cirrhatus, P. (?), A. tuberosus, Bull., and Hypochnus centrifugus, Tul., differs 
little from that of the first type. The chief difference is that the cell-walls in the rind 
are not a dark but a yellow brown; the surface of the rind is in most cases tolerably 
smooth, but in Hypochnus centrifugus it is uneven or felted over with the remains of 
the hyphae which surround the sclerotium in its younger state. The hyphae of 
the medullary tissue and their membranes are of varying thickness according 
to the species; they are in most cases chiefly filled with a watery fluid or with 
air; in Hypochnus centrifugus they contain drops of oil. I have never found 
tissue-elements of the host enclosed in the medulla even of those of the above 
mentioned sclerotia, which had developed in the interior of decomposing parts of plants 
(Mushrooms). 
c. A somewhat different structure from the above is seen in a sclerotium in 
Rabenhorst’s Herb. mycol. Nr. 1791, incorrectly named Sclerotium stercorarium, and 
of doubtful origin. Its white medullary tissue consists of thin-walled cylindrical 
hyphae which contain a watery fluid, and are usually rather loosely interwoven, 
the interstices being filled with air. Towards the surface the medulla passes gradually 
into an outer covering of many layers of narrower hyphae, which mostly run parallel 
to the periphery and form a tissue without interstices. The inner layers of this 
tissue are colourless, towards the outside the membranes become gradually yellow- 
brown, and those of the outermost layers are so considerally thickened that the lumina 
are much reduced in size. The whole sclerotium is thus surrounded by a firm uneven 
rind composed of several layers. 
d. The light-yellow Selerotium muscorum, which also belongs to some Agaric, 
consists of a web of broad thin-walled hyphae with narrow interstices containing air. 
The hyphae, which are not arranged in any order, are composed partly of elongated 
cylindrical and partly of short vesicular cells. The latter contain a clouded homo- 
geneous yellowish protoplasm, or a watery fluid in which drops of yellow oil are 
suspended. The surface of the sclerotium appears to the naked eye of a darker 
colour than the centre, but under the microscope the structure is seen to be the 
same throughout, and the medulla and rind are not clearly distinguished. Single 
surface-cells project here and there as cylindrical papillae. 
e. The snow-white medulla of the sclerotium of Coprinus stercorarius, Fr. has 
a similar structure to that in Sclerotium-muscorum. It is a pseudo-parenchyma 
composed of broad irregularly roundish or elongate-ovoid cells and single cylindrical 
hyphae; all the cells are very thin-walled and filled with a colourless, uniformly 
and finely granular, somewhat strongly refractive protoplasmic substance, which issues 
forth from injured cells and spreads through water and makes it turbid. These 
cells form a close tissue which is hard in the dry state, and has more or less 
narrow interstices filled with air. The cells of the medulla become suddenly smaller 
towards the circumference. The surface of the sclerotium is formed of a firm 
apparently black rind which is wrinkled in the dry state. Where this rind borders on the 
medulla it shows four or five irregular layers of small cells of the shape and size of the 
outermost cells of the medulla, but with brown membranes and apparently always 
clear watery contents. This layer is surrounded by the more superficial rind 
consisting of three or more layers of large cells usually of irregular roundish outline, 
which at the periphery have some resemblance to the largest of the cells of the medulla, 
and contain a watery fluid or air within a slightly thickened wall of a dark violet-black 
colour. Many of the superficial cells of the rind project irregularly above the rest 
