PTERIDOPHTTA. 195 



asexual generation, and upon it the spores are produced 

 from which new individuals of the first generation may be 

 developed. 



406. The first stage (called the prothallium) is composed 

 throughout of a few layers of soft tissue (parenchyma) 

 richly supplied with chlorophyll. From its under surface 

 root-hairs grow out into the soil. The sexual organs re- 

 semble those of the liverworts, and are antherids (producing 

 antherozoids) and archegones. They are generally pro- 

 duced upon the under side of the plant, and project slightly 

 from the surface. 



407. The fernworts are divisible into three classes, viz.: 



1. Stems hollow, jointed; leaves small. Equisbtin^. Horsetails. 



2. Stems solid; leaves mostly broad. Filicin^. Ferns. 



3. Stems solid; leaves small or narrow. LYCOPODiNiB. Lycopods. 



Class I. Equisetin^ {the Horsetails), 



408. In the plants of this class the plant-body consists of 

 a hollow elongated and jointed stem, bearing whorls of 

 narrow united leaves, which form close sheaths (s. Fig. 

 108); the stem is grooved, and is usually rough and hard 

 from the large amount of silica deposited in the epidermis. 



409. The branches, when present, are in whorls. Both 

 the main axis and the branches are in most cases richly 

 supplied with chlorophyll-bearing tissue; in some of the 

 species the stems which bear the spores are destitute of 

 cblorophyll. All the species have underground stems, 

 which bear roots and rudimentary sheaths, and which each 

 year send up the vegetating and spore-bearing stems. 



410. The Horsetails are perennial plants. In some species 

 the underground portions only persist, the aerial stems 



