PTERIDOPHYTES 



299 



like that already described for some herbaceous seed plants, and 



the young leaves spring from the apex of the stem and uncoil 



in the peculiar circinate manner shown in Fig. 167. They are 



often protected in the early stages of their development by the 



abundant scales, or 



ramenta (singular, 



r amentum), which 



are so character- 



istic of ferns. The 



roots (Fig. 168) are 



true roots, like those 



of seed plants, and 



not hairlike rhi- 



zoids like those of 



the moss group. 



The cell struc- 

 ture and the tissues 

 of the stem, roots, 

 and leaves of ferns 

 are also very simi- 

 lar to those of the 

 higher plants. In- 

 deed, ferns are the 

 first of the vascular 

 plants which possess 

 a true vascular conducting system composed of phloem and 

 xylem. For these various reasons they are now regarded as the 

 ancestors of higher seed plants. 



FIG. 168. Habit and parts of a single plant of Adiantum 

 a, the entire plant ; b, portion of a pinna 



SPOKOPHYTE 

 ADIANTUM (MAIDENHAIR FERN) 



Habit. The maidenhair fern is like the other members of the 

 Filicales, mentioned above, in having an underground stem, or 

 rhizome (Fig. 168), which is thickly covered with ramenta. These 

 scales are particularly abundant at the growing point and on the 

 young leaves, and serve as a protective covering. 



