258 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
tively large capsule of a general globose form. The wall of the 
capsule is composed of a single layer of cells and is usually deep 
brown in color. The cell walls are more or less thickened and often 
show trigones; annular and spiral thickenings, however, are absent 
altogether. The upper part of the wall forms a more or less distinct 
circular lid, which falls off intact or in fragments, leaving behind a 
cup-shaped portion with an entire or irregularly dentate or lacerate 
margin. 
The great importance of the spores in Asterella for taxonomic pur- 
poses has been emphasized by Howe. It must be kept in mind, how- 
ever, that the spores vary greatly in size, in color, and in surface 
markings, the differences often being due to var ying conditions dur- 
ing critical stages of development. Spores, for example, which 
would be large, deeply pigmented, and coarsely reticulated under the 
best conditions, might be much smaller, paler, and almost smooth if 
the conditions had been bad. Taking the genus as a whole, the spores 
are of a fair size and show a distinct tetrahedral form, the base being 
represented by a spherical triangle; upon this base the surface mark- 
ings usually attain their most typical development. The other three 
faces of the spore are plane triangles. On the six edges of the spore 
distinct membranous wings are present; these often vary consider- 
ably in width, even in a single species, and the wings bounding the 
spherical face are usually broader than the three wings formed at the 
junction lines of the plane faces. The outer wall layer, which of 
course yields the distinctive markings, is always more or less pig- 
mented with yellow, brown, or purple, and sometimes becomes so 
nearly opaque that the markings are difficult to demonstrate. These 
markings are of two types: fine, irregular points or lines, represent- 
ing local and often pigmented regions of thickening in the mem- 
brane; and coarser ridges, representing folds of the membrane. 
Sometimes the fine markings are the only ones present, and sometimes 
they anastomose to form a delicate and irregular reticulum. The 
coarser ridges in many cases unite to form a more regular reticulum, 
but they are often crowded together irregularly or unite vaguely and 
indiscriminately. The distinctive features of the spores will be con- 
sidered in greater detail in connection with the individual species, 
The pigmentation which is so characteristic of the spores usually 
affects the elaters also, although in a lesser degree. In most cases it 
is restricted to the spiral bands, but sometimes the rest of the wall 
is more or less colored, in rare cases to such an extent that the spirals 
are detected with difficulty. The number of spirals varies from one 
to three and is not always the same throughout the entire length of 
an elater. In A. elegans, for example, the middle portion usually 
*Bull, Torrey Club 25: 191. 1898. 
