438 SECOND PART.—MPCETOZOA. 
treatment with potash discloses an axile thread of an opaque substance, which turns 
yellow with iodine and is a remainder from the contents of the young tubes. The 
membrane of the tubes is thick but not evidently stratified, with a different degree of 
flexibility in different species, and coloured with different shades of yellow, red and 
reddish brown. It shows in all cases ridge-like projections or thickenings on the 
outer surface which run spirally round the tubes and often appear as folds in the 
membranes, since the lumen of the tubes is broader along their course and constricted 
in the intervals between them. The direction of the spiral as it ascends is with few 
exceptions, one only of which has come under my notice in Trichia varia, the same 
as that of the hand of a watch. The number of ridges varies with the species, being 
2in T. varia and 3-5 in T. fallax and T. chrysosperma. Variations of number in 
the same tube are partly due to bifurcation of the ridges, partly to the fact that 
some of them do not reach the end of the tube. In some species, as Hemiarcyria 
rubiformis, the back of the ridge is beset with spike-like processes. Trichia chry- 
sosperma has a number of smaller slender ridges running between the spiral ridges 
and parallel to the longitudinal axis of the tube, and connecting each pair of spiral 
ridges in a scalariform manner (Fig. 193 ¢). The tubes of the capillitium lie mixed up 
together in great numbers and folded many times in the sporangium. If they are 
dried or their water is extracted by alcohol, they stretch themselves out but never 
become quite straight; if moisture is restored they acquire still stronger curvatures, 
and the same phenomena are repeated each time that the moisture is changed. This 
hygroscopic motility and the spiral ridges recall the elaters of the Hepaticae, and 
the tubes of Trichia have therefore received the name of elaters. 
Certain species of Trichia and Arcyria, some of which have been already 
named, have the cavity of the stalk of the sporangium filled with vesicles or cells, 
which resemble spores but are larger and incapable of germination. They may very 
well be receptacles of excreta like the calcium carbonate-vesicles of the Calcareae. 
The sporangia of Stemonitis, Comatricha, Enerthenema, and their allies are also 
distinguished in the mature state by certain peculiarities. They are borne on the 
stalk described above as being of the thickness of a hair or bristle and narrowing 
gradually upwards ; this stalk passes through the base of the sporangium and occupies 
its longitudinal axis as a central column (columella), and either reaches the apex 
where it expands in Enerthenema into a membranous disk passing into the wall, or 
comes to an end below the apex and splits as it were into threads of the capillitium, 
Stalk and columella are hollow tubes, the cavity of which contains air and lumps of 
some organic substance. The wall is thick and marked with longitudinal wrinkles, 
and is coloured a dark brown throughout or has an outer layer colourless. The base 
of the stalk expands into an irregular membranous disk which rests on the substratum 
(Fig. 186). The primary branches of the dark-brown capillitium spring with a broad 
base from the whole outer surface of the columella, or as in Enerthenema only from 
the disk-like expansion at its extremity. These branches ramify repeatedly in every 
direction, and the ramifications become united into a net-work which has everywhere 
a large number of meshes. A large number of slender branches run from the meshes 
of the circumference only, and become attached by their free extremities to the wall 
of the sporangium. The structure of the stronger branches of the capillitium is like 
that of the columella, but their lumen is not in communication with the lumen of the 
