2l6 



THIRD GROUP. VASCULAR CRYPTOGAMS. 



An abundance of usually brownish or dark brown flat pluricellular hairs, which soon 

 become dried up, occurs on aerial creeping stems and on their leaf-stalks; these are 

 the chaff-scales or paleae which often quite conceal the buds and may be from one to 

 six centimetres in length (Polypodium, Cibotitirn, &c.). Long stout bristles appear 

 sometimes on the laminae of leaves, as in Acrosiichum crinihnn, and not unfrequently 

 fine delicate pluricellular hairs. 



The sporangia of Ferns are small roundish capsules with a long stalk in the 

 Polypodiaceae and Cyatheaceae, but sessile in all other Ferns. The 

 wall of the mature capsule is formed of one layer of cells ; a row of 

 cells in this layer running straight or obliquely across the capsule or 

 down its length is developed in a peculiar manner and forms the 

 annulus ; the contraction of the annulus by drying causes the capsule 

 to burst at right angles to the plane of the annulus ; in some cases 

 instead of the annulus an apical or lateral group of cells of the wall 

 is developed in a similar manner. 



The sporangia are usually collected in groups, each of which is 

 termed a sorus ; the sorus contains a small fixed number, or a large 

 indefinite number of sporangia, and between them occur not unfre- 

 quently delicate pluricellular hairs, \\-\eparaphyses. A luxuriant growth 

 from the leaf, the indusium, often covers over the entire sorus with a 

 kind of roof, or surrounds it as with a cup, or even incloses it entirely 

 as in a capsule. The indusium is often only an excrescence of the 

 epidermis, but in other cases it is formed by an outgrowth of the tissue of the leaf 



FIG. 163. Aspi- 

 diumFilix-mas. Un- 

 der side of a pinnule 

 showing eight indusia 

 i, twice the natural 

 size. 



FIG. 164. Aspidiinn Filix-mas. A transverse section of a leaf with a sorus consisting of the sporangia s and the 

 indusium ii; a small vascular bundle is seen on each side in the mesophyll of the leaf, the cells of the sheaths showing the 

 dark brown thickenings on the inner walls. B young sporangium with the annulus perpendicular to the plane of the 

 paper; r its uppermost cell ; four cells are visible in the interior, formed by division of the central cell. C side-view of 

 an almost mature sporangium ; rr the annulus, d the stalked gland peculiar to this species ; the young spores appear 

 just formed in the sporangium. 



itself, and is then composed of several layers of cells, and may even have stomata. 

 In the Lygodieae each separate sporangium is enveloped in a pocket-shaped formation 

 from the tissue of the leaf, as if in a bract ; in this case 1 the indusium grows up 



1 Piantl, Untersuch. ii. d. Gefasskryptogamen, Heft II. (Schizaeaceen). 



