PADINA. 



[ 486 ] 



PADINA. 



filled with a clear serous liquid, contained in 

 largest quantity in the central cavity of the 



Fig. 558. 



A human Pacinian corpuscle, a, stalk ; b, nerve-fibre 

 within it ; c, outer, d, inner layers of the sheath ; e, pale 

 nerve-fibre in the central cavity ; /, its branches and ter- 

 mination. 



Magnified 350 diameters. 



innermost layers. Each is also furnished 

 with a stalk, containing a slender branch of 

 a nerve, which passes from the stalk into 

 the central space, in the upper part of which 

 it terminates frequently in two or three 

 branches, each with a free granular tubercle. 

 The nerve-fibre contains no white substance. 



BiBL. Kolliker, Mikrosk. Anat. ii., and 

 the Bibl. therein. 



PADINA, Adanson. — A genus of Dictyo- 

 lacea; (Fucoid Algae), containing one species, 

 P. Pavonia (fig. 559), found rarely in sum- 

 mer and autumn on the south coast of Eng- 



land. The fan-shaped or reniform fronds 

 grow in tufts, and are 2 to 5" high, sometimes 

 entire, sometimes cleft (fig. 559). They are 



Fig. 559. 







Padina Pavonia. 

 Frond, one-third natural size. 



marked with concentric zones. The sub- 

 stance is parenchymatous, the number of 

 layers of cells diminishing with the thickness 

 and solidity from the base to the edges. 

 The back of the frond is covered by a layer 

 of cells much smaller than the rest, forming 

 a kind of epidermis, w^hich ultimately ac- 

 quires a thickish cuticular layer. The grow- 

 ing edge of the frond is rolled backwards 

 (circinate) and fringed. The fructification 

 occurs in linear concentric sori, on the co- 

 loured zones of the frond. The pear-shaped 

 spore-sacs (fig. 560) originate from cells of 



Fig. 560. 



Vertical section of a frond at a concentric zone, made 

 in a radial direction, cutting through the sorus of spore- 

 sacs and a line of hairs. The indusial layer of cuticle has 

 been omitted by the artist. 



Magnified 50 diameters. 



the epidermal layer, which take on special 

 development, and in the course of their 

 growth push up and finally burst through 

 the loosened cuticular layer which originally 

 clothed them, so that the latter form a kind 

 of indusium like that of the Ferns. The 

 spore-sacs produce each four spores, which 

 separate after their escape from the sac. 

 The zones of the sori alternate with zones 

 composed of tufts of jointed hairs placed ni 



