356 XXVI. REPRODUCTION OF THE PTERIDOPHYTA. 



dermis passes over into the indusium (i), which has the structure of 

 the neighbouring epidermis, except that it is wanting in stomata and 

 chlorophyll grains. In place of the latter it has small colourless 

 chromatophores. From the base of the furrow arise the sporangia 

 (sg) ; they can be seen in different stages of development ; each 

 derives its origin from a single epidermal cell. Even with a low 

 power (Fig. 130, A) we can distinguish in each sporangium a 

 stalk and a capsule, and on older ones a yellow-brown ring the 

 annulus can be noticed on the capsule. For further study we 

 use somewhat stronger magnification (Fig. 130, B). The stalk 

 passes over from a single to a double row of cells. The capsule 

 has an unilamellar wall of cells. As is shown by different views 

 of the wall of the capsule (B-E) the annulus is composed of a row 

 of projecting cells of this capsule wall, which, commencing at the 

 stalk, passes over the apex, and down the opposite side, and, 

 flattening and becoming broader, dies away before again reaching 

 the stalk. The inner and tranverse walls of the cells of the 

 annulus are strongly thickened and browned ; the thickening 

 decreases in the transverse walls in the direction of the outer 

 surface, and is wanting in the outer walls. The sporangium 

 opens between the broad cells in which the annulus ends (Fig. 

 130, C, E) ; the one half of these broad cells then lies on the one, 

 the other half on the opposite side of the fissure. The cause of 

 the rupture lies in the annulus, which in drying tends to diminish 

 its curvature. The brown wall of the ripe spore shows (Fig. F) 

 its outer surface covered with a network of cockscomb-like pro- 

 jections. 



Sorus of Aspidium. In Aspidium Filix-mas, the "male Fern," 

 we find indusia, kidney-shaped or sub-cordate, which with age 

 become leaden-coloured, and finally brownish, shrivel somewhat,, 

 and no longer completely cover the dark-brown sori. The spor- 

 angia have almost the same structure as those of Scolopendrium. 

 Upon some of them we see a short glandular hair, ending in an 

 unicellular head, arise from the stalk. The sporangia are attached 

 to a cushion-like prominence a placenta which lies over a stele. 

 To this latter adjoin reticulately- thickened trachei'des, which are 

 distributed in the placenta. At its apex the placenta bears the 

 indusium, attached by being curved down into the form of a stalk. 



Dehiscence of the Sporangia. If we take a preparation in 

 water which includes sporangia that are ripe, but still unopened, 

 and run in from the edge of the cover-glass a water-withdrawing 



