72 FOOTNOTES FROM 



supposed by some botanists to serve the same purpose in 

 the economy of the lichen as the bafk does in that of 

 the tree, viz., as a protection to the lower, living layer, 

 of the dead cellules of which it actually consists. In 

 some species this outer covering is smooth, and in others 

 covered with small hollows or pits, or with hair or 

 fibres, which serve to fix the plant. 



Nature has bestowed upon the lichens a peculiar mode 

 of reproduction, in which there is nothing analogous to 

 that of the higher orders of the vegetable kingdom ; and 

 yet they are propagated 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, of a different 

 colour from the rest of the plant, with which their sur- 

 face 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 deli- 

 cate flask-shaped cells, called thecse, containing 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 apothe- 

 cium or shield is wetted, the layer bearing the thecse 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 



