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varieties. The student will find in some works on lichens that, in an 
attempt at brevity, there has been an omission of some characters that are 
very essential to successful determinations and that in others the same end is 
gained by a dogmatic statement regarding form, size and color, which would 
lead the beginner to expect in the plants a like constancy, which by no 
means exists. 
The Apothecium. 
Likewise in the fruit, or apothecium, the main features of gross mor- 
phology are size, form and color : and these will now be taken up and con- 
sidered, one at a time. The apothecia are usually superficial and large 
enough to be seen easily with the unaided eye. But in some instances they 
are so small that they can be made out with difficulty with the hand lens. 
Or they may be immersed in the thallus and indicated at the surface by a 
slight elevation or depression as a disk or ostiole, or they may, when 
immersed, be scarcely discernable in any way except in sections of the thal- 
lus. From . i to 5 mm. is well within the range for diameters of apothecia. 
The apothecia are most commonly saucer-shaped or some slight modifi- 
cation of this form as when the disk is flat or somewhat convex instead of 
concave. In some instances the disk becomes very concave, when finally the 
apothecium may be called cup-shaped, and in others it is strongly convex, 
finally giving the apothecium a more or less spheroidal form. In all of these 
forms, the outline of a transverse section of apothecium would usually be 
very nearly a perfect circle ; but the form may become irregular as growth 
proceeds, so that at maturity this outline is quite irregular. In other lichens 
the apothecia are of some other form from the beginning. Thus there are 
the elongated and often branched forms such as are found in Gr aphis, and 
the difform or variously irregular forms as in Arthonia. Again, some 
apothecia are produced into a well developed perithecium, and these usually 
approximate a spherical form. 
The Disk. 
In those lichens in which the exciple is not produced into a perithecium, 
the upper surface of the apothecium is naked, except for a very thin film of 
thallus, which may persist . as an epithecium, a structure not mentioned in the 
descriptions of species. This upper and essentially naked surface, whether 
flat or more or less strongly concave or convex, forms the disk. The outline 
of the disk, then, may be circular or variously elongated or irregular, varying 
in this respect with the form of the apothecium as a whole. In color the disk 
varies considerably even in the same species. It is usually light colored in 
its early development and commonly becomes darker as it reaches maturity. 
The final color, then, may be a light or darker flesh-color or a light or darker 
shade of yellow, orange, red, brown, chestnut, olive, or even black. And 
the color is very seldom the same as that of the thallus, but the surface may 
be pruinose with a usually white powder, concealing the essential color of the 
disk. 
The Exciple. 
Below the disk is the hymenium, which may easily be made out in sec- 
tions with the hand lens. This structure is usually lighter in color than the 
