110 FIRST FORMS OF VEGETATION. 
gated with as unerring certainty and as great 
rapidity as the most prolific family of flowers. 
Every one who has an attentive eye must have 
often noticed the curious round disks or shields, 
usually of a different colour from the rest of the 
plant, with which their surface is often studded. 
These are called apothecia, and correspond with 
the flowers of the higher plants; for in them are 
lodged the seeds or germs by which the lichens 
are perpetuated. When examined under the 
microscope they are found to consist of a number 
of delicate flask-shaped cells, called thecz, con- 
taining 4, 8, 12, or 16 sporidia, that is, cells of an 
oval form, with spores or seeds in their interior. 
The mode in which these spores are ejected 
affords as wonderful a proof of design as was seen 
in the case of the ferns and mosses. It is 
principally in moist or rainy weather that this 
curious process is performed. When the entire 
apothecium or shield is wetted, the layer bearing 
the thecze or seed-vessels becomes bulged out 
above, whence arises a pressure on them, which 
ultimately bursts them at the summit, and causes 
the expulsion of their contents. Few things can 
exceed in beauty, as microscopical objects, the 
sporidia of many of the lichens. Some are bright 
scarlet, others deep blue, and others green, olive, 
golden yellow, or brown. 
