524 MANUAL OF NATUKAL HISTOEY. 



Aniheridia, and Pistillidia or Archegonia; and, 

 from late observations by Hofmeister, Suminski, and 

 others, the existence of sexuality among these plants 

 is rendered highly probable. 



Acrogens comprehend first the Ferns, numbering 

 more than two thousand species, in which the fronds 

 seem to represent branches, and the ramenta true 

 leaves; these are often diminutive and inconspi- 

 cuous in northern regions, but in tropical and sub- 

 tropical climes, they are frequently arborescent, 

 raising, at times, their graceful forms to the height 

 of thirty or forty feet ; next, the Club-mosses and 

 Pepper-worts small herbs, with a world-wide dis- 

 tribution ; and lastly, the True-mosses, including 

 the Liver-worts and Horse-tails, nearly equalling 

 the Ferns in multiplicity of species, some of which 

 are said to form the first appearance of vegetation 

 on a new soil, and to be among the last occupants of 

 exhausted lands or of an inappropriate clime. 



This class supplies man with but few useful 

 plants. The roots of some Ferns are esculent and 

 one species, Nephrodium (Aspidium) Filix-mas, is 

 employed in medicine. The powdery contents of 

 the spore-cases of some species of Lycopodium are 

 highly inflammable, and, under the name of vege- 

 table-sulphur, or witch-meal, are used in pyro- 

 techny. 



I. CLASS. ACROGENS (Acrogense). 



Stem and leaves distinguishable ; surface fur- 

 'nished with stomata. 



