- 88 - 
disk and is composed of paraphyses and asci. Below the hymenium is 
the hypothecium, often darker in color than the hymenium above it, so that 
the line of demarkation between the two structures may easily be made out 
with the hand lens. The hymenium and the hypothecium are hardly to be 
studied macroscopically, and are mentioned here mainly that another struc- 
ture, the exciple, may be located with reference to these two structures. 
Then the exciple may be said to form the saucer-shaped or cup-shaped cov- 
ering around the hymenium, being an upward continuation of the hypothe- 
cium on all sides. Such rather is th e proper exciple , but there is sometimes 
outside of this, or more often replacing it, what is known as a thalloid exci- 
ple. This last is similar to the th alius in structure and usually of the same 
color, while the proper exciple is never of the same color as the thallus and 
usually approximates in color the disk. 
Either of the exciples may be permanently absent, and either or both 
may be quite evanescent and only to be seen in young apothecia. But 
usually one is permanent or tardily disappearing so that it may be seen read- 
ily with the eye or the lens, and the nature and degree of development and 
permanence is of considerable value in the classification of lichens, even to 
the determination of species. The perithecium has been mentioned, and this 
is simply a produced exciple found in some lichens, and growing completely 
around the upper part of the hymenium, except the small opening or ostiole 
at the summit. The margin of a proper exciple is usually about at the level 
of the outer margin of the disk, or it may be somewhat raised above the disk. 
This margin is almost always quite entire, while the margin of a thalloid 
exciple is frequently crenulate, crenate, variously branched, ciliate or 
irregular. 
Position of the Apothecia. 
Perhaps the only thing yet remaining to be said regarding the fruit, is 
something concerning its position with reference to the thallus. Sometimes 
the apothecium is raised on a slender upward extension of the thallus, a short 
stalk or pedicel, quite different from the podetium of a Cladonia or the stipe 
of a Calicium and most frequently met in the larger foliose lichens. The 
stalk may be absent and the apothecium attached to the thallus at the centre 
of the ventral side of the apothecium. Such apothecia are said to be ses- 
sile. Again, the apothecium may be more closely attached to the thallus by 
all of its lower side, and then it is said to be adnate. Finally, the apothe- 
cia may be more or less immersed in the thallus, sometimes deeply, so that, 
when the disk is more or less over-grown by the thallus or by a perithecium, 
the structure is often quite obscured. 
The developement of the apothecium begins below the surface of the 
thallus, and the tendency in general is to become more and more superficial 
as maturity is reached. So it comes about that the apothecium sometimes 
remains permanently more or less immersed, or more commonly becomes 
superficial or stalked. And somewhat varying conditions as to position with 
reference to the thallus may be expected in many species. 
