THE FERNS 



537 



the lowest cell gives rise to the first leaf. A later stage in the de- 

 velopment of these parts is shown in Fig. 365, B. Covering the 

 growing tip of the root, somewhat as a thimble covers a finger tip, 

 is a protective organ termed the root-cap. Such a thimble-like cover- 

 ing continually renewed by the meristem which it protects is char- 

 acteristic of true roots. Root-hairs for absorption are soon devel- 

 oped. The leaf (Figs. 365, B, 362, B) soon differentiates into petiole 

 and blade, and curves so as to drag the tender leaf-tip up out of 

 the ground. An extreme curving of this nature performed by every 



^ 



'^S^K^MfM 



Fig. 363. — Fern Antheridium {Pteris sp., Polypody Family, Polypodiacew), 

 ^l". (Luersscn.) 



Fig. 364. — Fern Archcgonium {Osmunda sp., Royal-fern Family, Osmuyida- 

 cem). A, first stage viewed from above, -Y. B, same, cut vertically to 

 show the central cell (c) from which the egg is formed, and the cells {h) 

 which give rise to the neck, '-;!>. C-E, older stages, showing canal 

 cells (^c, 6c). /^, neck with mouth closed. G, same, top view. //, same, 

 mouth open. J, same as E but with egg-cell (e) ready for fertilization. 

 (Luerssen.) 



branch of the developing leaves gives us the familiar crozier-like 

 vernation characteristic of ferns. In the axis of the stem soon ap- 

 pears a central cylinder of prosenchyma which developing also in 

 the root and the leaf serves as a channel for conducting solutions 

 absorbed by the root to the green food-making parts of the leaf, 

 and likewise dissolved nutrients from the leaves to the stem and 

 the root where they may be used in growth or stored as a reserve. 

 As the stem grows larger, and leaves and roots become more numer- 

 ous, its central cylinder becomes a hollow cylindrical net-work of 

 broad flat meshes (Fig. 366), giving off slender branches to the 



