^r^6 VASCULAR CRYPTOGAMS. 



It may be mentioned here in addition, as an isolated histological peculiarity, 

 that in Aspidhmi Filix-mas, according to Schacht, roundish stalked glands occur in 

 the fundamental tissue of the stem, which I have also noticed in the green paren- 

 chyma of the leaves, and on the pedicels of the sporangia of the same Fern 

 (Fig. 266, C, d). 



The lamina of the leaf consists in Hymenophyllaceas only of a single layer 

 of cells, as in Mosses ; in all other Ferns it is formed of several layers. Between the 

 upper and under epidermis lies a spongy parenchyma containing chlorophyll, the 

 Mesophyll, penetrated by the fibro-vascular bundles which form the venation of the 

 leaf. The epidermis of Fern-leaves is distinguished by containing chlorophyll, and 

 by the peculiarities of the stomata already spoken of in the part of this work relating 

 to tissue (Fig. 76, p. 89). The course of the veins is very various ; sometimes 

 they run branching dichotomously at acute angles, or spreading like a fan upwards 

 and sideways, without anastomosing and without forming a mid-rib ; more often 

 the undivided lamina, or a division of the lobed, incised, or pinnate leaf, is 

 penetrated by a distinct median vein though but slightly projecting, from which 

 spring more slender branches, which themselves again ramify monopodially or in 

 a forked manner, and run to the margins. The finer veins frequently anasto- 

 mose like those of the leaves of most Dicotyledons, and divide the surface into 

 areolae of characteristic appearance. 



The Trichomes of Ferns are produced in a great variety of positions. True 

 root-hairs, simple unarticulated tubes, arise, not only on the roots themselves, but 

 also on underground stems and on the bases of leaf-stalks (as in Pteris aquilina 

 and Hymenophyllaceae). On aerial creeping stems and on the leaf-stalks the 

 numerous usually brownish or dark-brown flat multicellular hairs, the Palece, occur, 

 soon becoming dry, often entirely enclosing the buds, and attaining a length of 

 from I to 6 cm. (as in Polypodium, Cibotium, &c.). Long strong bristles are 

 sometimes found on the lamina (in Acrostichum crimtum), and very often fine, 

 delicate, articulated hairs. Finally, the sporangia themselves are trichomes. 



The Sporangia of Ferns are, from a morphological point of view, trichomes of 

 the leaves. They arise from epidermal cells, and are usually stalked capsules, the 

 wall of which, when mature, consists of but a single layer of cells. A ring of cells 

 belonging to the wall of the capsule and running across or obliquely or lengthwise 

 is generally developed in a peculiar manner, and is then termed the Aniitdus. By 

 its contraction when dried up the capsule bursts (at right angles to the plane of 

 the annulus). Sometimes, instead of the annulus, a terminal or lateral group of 

 the cells of the wall of the capsule is developed in a similar manner. 



The sporangia are generally combined into groups, each group being termed a 

 Sortis ; the sorus contains either a small definite number or a large indefinite 

 number of sporangia, and among them also very commonly some slender articu- 

 lated hairs, the Paraphyses. The whole sorus is very generally covered by an 

 excrescence of the epidermis, the true hidusium ; in other cases the false indusium 

 consists of an outgrowth of the tissue of the leaf itself, and is then composed of 

 several layers, and even has stomata; or the covering of the sorus is simply the 

 result of the margin of the leaf being recurved or rolled over it. In Lygodium each 

 separate sporangium is covered by a pocket-shaped growth of the tissue of the leaf 



