— 69 — 
securing wide distribution of sorediiferous lichens. Even when no Algae are 
present, as on freshly exposed rock surfaces, soredia may establish them- 
selves. 
The apothecia, or proper fruit of our typical lichen, consists essentially 
(see Fig. 4) of (1) a number of short hyphal branches perpendicular to the 
surface, and compacted into 
a dense layer, called the 
hymenium . (Hm.), which 
arises from (2) a denser 
tangle of hyphae, termed the 
hypothecium (He.). The sur- 
face of the hymenium is 
called the disk (Dk.). These 
parts (in Parmelia) are more 
or less enveloped by a con- 
tinuation of the thallus (com- 
pare Fig. 2), called the thal- 
tine exciple (Th. Ex.). 
The hyphal branches 
which compose the hyme- 
nium are of two sorts: (1) 
slender filaments ( paraphy - 
ses , Pa., Fig. 5), each end- 
ing at the surface in a col- 
ored knob, and (2) club- 
shaped sacs {thekes or thecce, 
Tk ) each of which contains 
when mature usually eight 
minute bodies known as 
spores (Sp.) The spores are 
reproductive bodies, each 
capable under suitable con- 
ditions of growing into a 
lichen-fungus like the pa- 
rent. In our Parmelia the 
spores (Fig. 6) are simple 
cells, ellipsoid in form, and consist of a delicate transparent wall (Wl.), 
enclosing gelatinous (protoplasmic) contents which are colorless or but 
faintly tinged. The paraphyses besides affording some protection to the 
young thekes during development, aid in the ejection of the spores. Under 
the influence of moisture the paraphyses swell, and thus press upon the 
ripe thekes so that the apices are ruptured and the spores squeezed out with 
considerable force. A melon seed pressed between thumb and finger, illus- 
trates well what happens. 
Dk. Tic-. 4. 
Fig. 4. 
The same. Vertical section of apothecium, 
magnified about 50 diametres. Th., Ex.,thal- 
line exciple: He., hypothecium: Hm., hyme- 
nium: Die 'Dsk 
Fig-. 5. 
Fig. 5. 
The same. A portion of the hymenium, 
magnified about 350 diametres. Pa., para- 
physes; Tk., theka: Sp., spore; He., hypo- 
thecium. 
Fig. 6. 
The same. A spore, magnified about 1,000 
diametres. Wl., wall. (Original.) 
(To be Continued . ) 
Cambridge, Mass. 
