24 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
relation to the growth of the thallus and perform the function of 
assimilation for the fungal hyphe. 
THE APOTHECIUM IN GENERAL. 
The fruit of a lichen is commonly called an apothecium, and con- 
sists of an epithecium, a hymenium, a hypothecium, and a thalloid 
or a proper exciple or both. Hither or both of the exciples, however, 
muy disappear, or the proper exciple may be produced into a strue- 
ture known as a perithecium. Also, when a perithecium is present, 
it sometimes incloses an additional structure known as an amphithe- 
cium. These structures may now be explained in order. 
THE EPITHECIUM. 
This structure is supposed to be a film of the thallus extending 
over the upper surface of the apothecium, and its presence is explained 
by the fact that the development of the apothecium begins within 
the thallus and that the overlying part of this is carried up with the 
apothecium as it finally bursts through the upper cortex of the thallus. 
The epithecium is of the same color as the upper portion of the hyme- 
nium and is usually, when present, not distinguishable from. it. 
Indeed, many of the older lichenists considered this portion of the 
hymenium a part of the epithecium and spoke of the epithecium as 
having certain colors, when the color was in the upper portion of the 
hymenium. In the descriptions to follow the epithecium has been 
ignored as something too rudimentary to be distinguished in an ordi- 
nary examination of a fruit, or, as probably in the large majority 
of instances, entirely absent in mature apothecia. Special statements 
are made, however, of the color of the upper portion of the hyme- 
nium when differing from that of the lower portion. 
THE HYMENIUM. 
The hymenium is composed of the asci or spore-containing sacs, 
and the protective filaments called paraphyses (fig. 9, 5, p. 62). In 
position this structure lies below the epithecium and above the hypo- 
thecium. The asci are always thicker and usually shorter than the 
paraphyses, and the mature spores may usually be distinguished in 
them more or less plainly. It need be further stated here only that 
the asci and paraphyses usually are erect or suberect and constitute 
a densely packed mass composed of the two tissues. 
THE THALLOID EXCIPLE. 
This structure is commonly found in lichens having a well-developed 
thallus, whether fruticose or foliose, and is found, therefore, most com- 
monly in the foliose lichens and least commonly in the crustose ones, 
In structure the thalloid exciple resembles the thallus (fig. 14, 6, 
p- 178), with which it is always continuous. The outer layer of such 
