CHAPTER V.--COMPARATIVE REVIEW.—GASTROMFCETES. 315 
unicellular threads with the primary stem fusiform and simple or divided into a 
few branches and beset, especially at the extremities, with short pointed branches like 
spikes. 
Geaster hygrometricus is the only one of the species in question with which I 
am acquainted in which the mature capillitium forms a connected net-work. The 
much branched, often torulose and unusually thick-walled threads wind in and 
out confusedly among one another, and their extremities are often swollen into a 
head and adhere firmly together. Like the earlier observers I found no true capillitium 
in Scleroderma, only the walls of the chambers dried up and disorganised. Sorokin 
speaks otherwise on this point, but it is possible that he was not examining the same 
species. 
The Zeridium of Scleroderma is thick and leathery, but it has much the same fibrillose 
structure as the Hymenogastreae described above. 
In Lycoperdon, Bovista, Mycenastrum, Geaster, Sclerangium, &c. the wall 
of the peridium is differentiated into two concentric separable layers, peridium interius 
and exterius. The inner layer is usually a thin membrane of the consistence of paper, 
but in Mycenastrum it is cork-like and more than two millimetres in thickness. In 
Bovista, Geaster, and species of Lycoperdon, the latter of which require more 
exact investigation, it consists of several layers of stout hyphae which run in the direc- 
tion of the surface and are firmly intertwined, having generally the structure and appear- 
ance of capillitium-threads. In Geaster hygrometricus the elements of the peridium are 
exactly like those of the capillitium, and are continuous with them, and the capillitium-net 
is therefore concrescent everywhere with the peridium. Inall the species of Lycoperdon 
which have been examinedand in Geaster fimbriatusand G. fornicatus thehyphaeare distin- 
guished from the capillitium-threads by their smallersize and clearer colour, but they send 
countless branches into the interior of the peridium, which, as long as they are free, have 
all the characters of capillitium-threads. The inner peridium of Bovista plumbea has a 
similar structure and the same dense woolly covering on the inner surface formed of 
threads which have their origin in the weft of the peridium ; but these do not resemble 
the capillitium-threads, nor are they connected with them, but are long fine tapering un- 
branched hyphae. The inner peridium of Mycenastrum Corium is a dense irregular air- 
containing weft of hyphae with brown membranes, more finely fibrillose and denser 
in the outer region than in the inner. The hyphae end on the inner surface in pointed 
branches which resemble but are always more slender than the capillitium-threads. 
We know from descriptions that the inner peridia of most forms, Geaster for 
instance especially, ultimately open in a fixed manner at the apex and discharge 
the spores. The anatomical conditions which lie at the bottom of the process 
have not been thoroughly examined. Where the inner peridium passes into a central 
column or a sterile basal portion of the gleba, these parts, so far as they have been 
examined, are found to have essentially the structure of the trama. The stalk-like 
projecting basal portion of Lycoperdon has chambers like the gleba, but the walls 
of the chambers are sterile or furnished only with insignificant traces of basidia. 
The outer peridium in Mycenastrum is a whitish soft thin membrane covering the inner 
peridium and composed of a loose weft of colourless thin-walled cylindrical hyphae ; 
when mature it peels off in lobes and at length leaves the inner peridium uncovered. 
“The peridium externum is more highly developed in Lycoperdon and Bovista. In 
these genera it is formed of large-celled usually pseudo-parenchymatous tissue, which 
in some cases, as Bovista plumbea, is seen to consist of several layers and often has 
external projections in the shape of warts, spikes, &c. In the young state it adheres 
firmly to the inner peridium, the elements of the two passing into one another. 
At maturity, when the copious excretion of water already described takes place in 
the compound sporophore in forming the spores, the inner layer of the outer peridium 
becomes disorganised and is changed into a slimy or fluid mass, which soon dries 
up or is absorbed, and hence the outer peridium often peels off from the inner and 
