102 



ELEMENTARY BOTANY. 



Fig. 127. 



hairs or scales. 



develops into a leafy plant of considerable size, with marked 

 differentiation of tissue, and capable of producing non-sexual 

 spores. 



17. True roots first make their appearance in the Pterido- 

 phytes. They, like the stem, develop from a triangular apical 

 cell (Fig. 127, Ap.). This gives rise behind to the tissue of 



the root, and in front to the root- 

 cap (Fig. 127). The three systems 

 of tissue — epidermal, fibro-vascular, 

 and fundamental — are well devel- 

 oped. The epidermis contains sto- 

 mates of the ordinary kind. Tri- 

 chomes or hairs are often abundantly 

 developed, especially on young leaves 

 when they take the form of scurfy 

 The Pteridophytes are divided into three 

 classes : the Ferns {Filices), the Horsetails, or Scouring Rushes 

 (Equisetaceas), and the Club-mosses 

 (Lycopodiaceas). 



18. The Ferns have a solid stem, 

 with roots and broadly expanded 

 leaves. They are mostly terrestrial, 

 and all richly supplied with chloro- 

 phyll. The spores are developed in 

 sporangia on the surface or margins 

 of the ordinary or modified leaves. 

 The leaves, usually called fronds, are 

 circinate in their unfolding, and often 

 divided and several times compound. 

 On their under surface are the sori, 

 or clusters of sporangia (Fig. 128). 

 Each sorus may be naked, or it may 

 be covered by a membrane, called 

 Fig 128 ^^^ indusium (Fig. 128). This is of 



various shapes, and has various modes 

 of attachment in the different genera. The sporangia are gen- 

 erally roundish and pedicelled bodies. Each sporangium, in 



