544 



FILICES. 



(fig. 770), which creeps along or under the surface of the ground, 

 emitting descending roots and ascending fronds (leaves), or which rises 

 into the air so as to form an acrogenous trunk (fig. 116). This trunk 

 (stipe) is of nearly uniform diameter, is hollow in the interior, marked 

 on the hard outer rind by the scars (cicatrices) of the leaves, and con- 

 tains vascular bundles of woody, dotted, and scalariform vessels, which 

 are enclosed in hard plates, and are arranged in an irregular manner 

 (fig. 117). Sometimes the trunk is dichotomous (fig. 118). The outer 

 fibrous covering is formed by the bases of the leaves, and is thicker at 

 the lower than at the upper part of the stem. The leaves (fronds) have 

 a circinate (gyrate) vernation (fig. 7 70 y _/"'); their veins are generally 

 of equal thickness, and either simple or dividing in a forked manner 



(fig. 771), or somewhat reticu- 

 lated, and occasionally stomata 

 occur. Reproductive organs, 

 consisting of spore-cases (thecse, 

 sporangia), which arise from the 

 veins on the under surface of 

 the fronds (figs. 770 /'", 771 s, 

 772), or from their margin. 

 Spore-cases, either stalked, with 

 the pedicel passing round them 

 in the form of an elastic ring 

 (fig. 773), or sessile and desti- 

 tute of a ring. The thecse some- 

 times arise from the surface of 

 the frond, while at other times 

 they spring from below, hav- 

 ing a cuticular covering in the 

 form of an indusium or invo- 

 lucre (fig. 771). The clusters 

 of thecse are called sori (fig. 

 772). The margin of the frond 

 sometimes is folded so as to 

 cover the thecae, and at times the 

 whole frond is converted into 



Fig. 770. Rhizome of Scolopendrium offlcinale, with several fronds 0eaves), /', /", /'", /"", 

 in different degrees of development. In /' and/", the circinate or gyrate vernation is seen. In 

 /"", the linear transverse sori or clusters of thecae are seen, having the appearance of dark lines 

 on the lower surface of the frond. 



Fig. 771-773. Frond and fructification of Polystichum angulare, to illustrate the natural order 

 Filiees. 



Fig. 77L Part of the frond seen on the lower surface, p. Two pinna covered with son, s, 

 having an indusium. r, Rachis or central stalk of the frond. 



Fig. 772. One of the sori or clusters of thecse cut vertically, n, The vein bearing it. t, In- 

 dusium or fold of the frond covering it c, Thecae or sporangia (spore-cases). 



Fig. 773. One of the thecse separated at the period of dehiscence. a. Incomplete annulus or 

 ring, which is elastic, and causes transverse dehiscence of the theca. p, Stalk of the theca. *, 

 Spores discharged. 



