PTERIDOPHYTA. 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. EquiseTiIna%. Horsetails. 
2. Stems solid; leaves mostly broad. Fiuicina. Ferns. 
8. Stems solid; leaves small or narrow. Lycoroprna. Lycopods. 
Crass I. Eguiserina (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 
chlorophyll. 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 
