602 



HUTCHINSON'S POPULAR BOTANY 



FIG. 638. MALE FERN. 



A pinnule, or lobe. of a pinna. The 



roundish scales are indusia covering 



thesori. 



divisions or teeth of a membranous sheath : in 

 Isoetes (Selaginellacese). Pilularia (Rhizocarpese), 

 and Phylloglossum (Lycopodiacese) they are long, 

 narrow, and awl-shaped. In some ferns the 

 barren and fertile leaves differ from one another 

 in appearance and especially in the degree of 

 division of the lamina. In Salvinia they are of 

 two kinds, one floating on the surface of the water 

 and entire ; the other submerged, very finely 

 divided, and performing the functions of a root ; 

 in Azolla (Rhizocarpee) they are floating and 

 bilobed. In some genera of Filices and their 

 allies the leaves are quite entire ; in the Hymeno- 

 phylleae they are very delicate, consisting of only 

 a single layer of cells, and in the smaller species 

 closely resemble those of the foliose Hepaticse; 

 while in most ferns they are of considerable (in 

 the tree-ferns of gigantic) size, with well-marked 

 petiole, rachis, and lamina, and distinguished by 

 the great extent to which the lamina is divided. In most cases (except the 

 Hymenophyllaceae) they are abundantly provided with stomates. The tissue 

 beneath the epiderm consists of a parenchyrnatous mesophyll containing 

 abundance of chlorophyll, the portion of which adjacent to the upper 

 epiderm is frequently developed as palisade-parenchyme. This mesophyll 

 is permeated by 'vascular' bundles or veins, 

 which branch off from the cauline bundles, and 

 are distinguished in the majority of ferns by their 

 dichotomous mode of branching, in contrast to the 

 reticulate anastomosing in Dicotyledons, and the 

 parallel arrangement in most Monocotyledons. 

 Among Gymnosperms a similar arrangement is 

 presented by Salisburia and Stangena. The floral 

 metamorphosis of the leaves of Flowering Plants 

 does not occur in Vascular Cryptogams, nor their 

 special agglomeration round the organs of repro- 

 duction as in Mosses." 



The spore-case (spwange) varies greatly in the 

 different families, and is variously grouped, but 

 there is more uniformity in the origin of the spore 

 itself, which is produced much in the same way 

 as the pollen-grain of Flowering Plants. A sin- 

 gle cell, or group of cells, shows by the nature of 

 its contents at an early period that it differs from 

 the surrounding cellular tissue. It is known as 



FIG. 639. MALE FERN. 



(a) A sorus covered by its indusium. 



(6) A sporange splitting to set free 



the spores (cc). 



