154 SYSTEMATIC BOTANY. 



178. True roots first make their appearance in the 

 Pteridophyta. They, like the stems, develop from a tri- 

 angular apical cell (Fig. 266). This gives rise behind to 

 the tissue of the root, and in front to the root-cap (Fig. 

 266, R.c). The three systems of tissue — epidermal, fibro- 

 vascular, and fundamental — are well developed. The epi- 

 dermis contains stomates of the ordinary kind. Trichomes, 

 or hairs, are often abundantly developed, especially on 

 young leaves, when they take the form of scurfy hairs, 

 or scales. The fibro-vascular bundles are always closed. 

 They generally contain tracheary, parenchymous, and 

 sieve-tissue. The fundamental 

 tissue consists of parenchyma, 

 and sometimes also ' scleren- 

 chyma; collenchyma and lati- 

 ciferous tissue are seldom met 

 with. The Pteridophyta are 

 divided into three classes: (1) 

 the Horsetails, or Scouring Rushes (Equisetinece), (2) the 

 Ferns {Filices), and (3) the Club-Mosses (Lycopodinex). 



I. Equisetineae. The plants (non-sexual generation) of 

 this class (called Horsetails, or Scouring Rushes) have a 

 hollow-jointed, grooved stem, bearing at each node a whorl 

 of narrow, united leaves, which form a sheath. The 

 branches arise in the axils of the leaves, and are, there- 

 fore, verticillate. There are' underground perennial stems, 

 which each year send up the vegetative and spore-bearing 

 stems. The spores are produced in sporangia, which are 

 modified leaves on the ends of the ordinary green stems, or 

 on early colorless or brownish stems, which die as soon as 



Fig. 266. Diagrammatic section tiirough the tip of a Fern root^ showing the apical 

 cell {afi) and the root-cap (H.c). 



