VILIVES. 



373 



the macrosporangia usually containing only one macrospore. 

 Sporangia in clusters, enclosed in modified leaves or 

 "fruits." 



Order Filices, the true Ferns. Tlie protliallia of the Kerna are 

 green thallus-like structuree, growing upon the surface of the ground. 



Kg. 257a.— Longitudinal section of the apex of the root of Pteris hastata. r, 

 apical cell ; o, 0, epidermis ; e, cortical tissue ; c-c, c-o, the primary fibro-vascular 

 bundles ; n, m. I, k, the root-cap ; k, /fc, daughter-cells recently cut off from the apical 

 cell.— After Nfigeli and Leitgeb. 



and composed at first of but a single row of cells, but later of extended 

 layers of cells. Th^v are moiiceciMua, and bear their antheridia on the 

 basal portion of tb^ under surface, while the archegonia are found near 

 the apical margin of the same surface. After fer- 

 tilization the germ-cell divides into four parts, the 

 uppermost one (or two) of which becomes the foot, 

 or organ which remains in contact with the prothal- 

 lium ; one of the other parts develops into the first 

 root, and the other into the first leaf. The young 

 plant is thus formed on the under side of the pro- 

 tliallium, from which it grows up as shown in Figs. 

 256 and 255. 



The stems of Ferns are mostly short, or slender 



and creeping in our species, but in the tropics they ,I'>g.^ 2576. —Portion 



„. ° ■ J , 1 1 ■ 1 ^ J ,, . , ■'of under surface of a 



are often of considerable height and thickness, leaf of Folypodlum. 



some tree-ferns attaining the height of 24 metres Le''^alut°"aiid^ De' 



or more (80 feet or more). They increase in length caisne. 



only, and this takes place by the continued division of an apical cell 



They contain flat fibro-vascular bundles (Fig. 257, A and B), which are 



usually disposed in a single circle, as seen in a cross-section, but in 



some cases there are bundles in the medullary portion also. On ac- 



'•ount of the presence of thick masses of thick-walled cells, (scleren- 



