30 



usually ellipsoid, but may be of any shape, and are simple, 

 or divided into sporidia by one or more transverse partitions • 

 tbey are then called septate. 



Tbe spermagones are microscopic, simple, or compound 

 cavities in the thallus, opening by pores, whose orifice is 

 usually dark. They are full of gelatine, and contain sterig- 

 mata, which are simple or branched, articulate or inarticu- 

 late filaments, short, straight : articulate sterigmata are 

 called arthrosterigmata. Upon the sides or tips of the 

 sterigmata are the spermatia, which are most minute, ovoid, 

 ellipsoid, linear or acicular, straight or curved colorless bodies. 

 The sp)ermatia accumulate in the cavities of the spermagone, 

 and escape by its j^ore. They apj^ear to be analogous to the 

 antherozoids of Algce, etc., but have no cilia, and are not 

 developed into antheridia. They are found in maturity 

 usually in spring or summer, long before the spores of the 

 apothecium are mature, and the relations between these two 

 kinds of organs are still disputed. 



Pycnidea are longer, thicker walled, sometimes superficial 

 spermagones, of which the sterigmata are simple, inarticulate, 

 tubular, tapering pedicels, called stylospores, that bear at 

 their tops bodies analogous to spermatia, but longer, curved, 

 oblong, and full of granular contents. 



In germination, the sporidia of a Lichen give off one or 

 more branching filaments, whose branches interlace, and 

 form a network, upon the hyjjothallus, which again developes 

 into the medullary stratum. A layer of colorless cells next 

 spreads over the liypothallus, and amongst these the gonidia 

 appear. In many Lichens, including most of those growing 

 on bark, there is no further development of thallus, the 

 apothecia growing from this, and in some few the hypo- 

 thallus is alone formed. In the higher forms, however, 

 a cortical layer is added. The liypothallus though often 

 evanescent, is present as the fibrils of Stida, the black fringe 

 of Lecidea geographica,. and in other forms or colors in many 

 other corticolous and rupicolous s]3ecies. The food of Lichens 

 is not confined to the gaseous elements, for they take uj) 

 mineral matter in abundance, especially carbonate and 

 oxalate of lime, besides compounds of alumina, silica, iron, 

 potash, soda, magnesia, and even of metals as manganese 

 and iron. Some species attain a great age, and some aj^pear 

 to burrow into the rock they inhabit. This burrowing has 

 been attributed to the corroding power in the vegetable, but 

 Dr. Hooker thinks it more probably due to the moisture they 

 retain around them. With reference to the age, the Eev. 

 Mr. Berkeley thinks that the growth is very rapid at first. 



