282 Lister . — On Chondrioderma difforme 
from a fraction of a millimeter to 2-4 m.m. in diameter 
(Fig. 1). 
Under ordinary conditions, the sporangium is found attached 
throughout its lower surface to a leaf by means of a mem- 
branous wall possessing a thickened margin of a more or less 
deep orange colour (Fig. 2). Adnate to this wall is a layer, 
usually of a purplish tint, which gives rise to the capillitium, 
and extends upwards as a delicate membrane enclosing the 
spore-cavity ; numerous aggregations of chalk-granules are 
embedded between these two basal layers ; outside the 
delicate upper membrane, and often extending on to the leaf 
slightly beyond the thickened margin, is a thin eggshell-like 
crust composed of crystals of calcium carbonate, usually 
closely compacted together. This outer calcareous wall is 
either attached to the upper membrane, or, less frequently, 
is separated from it by shrinking of the interior, and stands as 
a somewhat domed roof with a more or less considerable 
intervening cavity. 
The capillitium extends among the mass of spores, con- 
necting the lower with the upper part of the inner membrane, 
and consists of flattened threads, broad at their base and 
forking again and again into delicate extremities ; the threads 
are sometimes filiform and anastomosing, either uniform or 
with expansions containing granules of calcium carbonate 
or refuse matter ; they are often interrupted with dark bands 
or knots, such as are commonly seen in the capillitium of the 
genus Didymium. The colour of the capillitium varies from 
deep purple to pale yellow; or both the stout and delicate 
forms may be colourless. The spores measure 10-14 M and 
are smooth, of a dark brownish purple colour ; one side of the 
spore is usually thinner and paler in tint than the other, and 
is marked with a few reticulated dark lines. In drying, the 
paler side contracts towards the thicker and darker one, which 
retains its rounded form ; it is along the lines of reticulation 
that the spore-wall breaks on the emerging of the swarm- 
cell. 
In order to follow carefully the development of the 
