SPIRAL STRUCTURES. 



[ 594 ] 



SPIRAL STRUCTURES. 



The layer of cells lining the ANTHERS of 

 Fig. 670. Fig. 671. Fig. 672. 



Fig. 670. Annular-fibrous cell from the stem of Misle- 

 toe. Magnified 200 diameters. 



Fig. 671. Cell intermediate between reticulated and 

 pitted, from the Misletoe. Magnified 200 diameters. 



Fig. 672. Spiral-fibrous cell from the leaf of an Orchid. 

 Magnified 200 diameters. 



Flowering plants are characterized by most 

 varied patterns of spiral markings (PI. 32. 

 figs. 1-5) ; in these cells, moreover, we some- 

 times see the connexion between the fibrous 

 and homogeneous deposits well illustrated, 

 as the cells may have one or more sides 

 marked with spiral fibres, while the remainder 

 of the wall is covered with a continuous 

 layer. A similar structure, generally with 

 perfect spiral fibres, occurs in the walls of 

 the sporanges of Jungermannia, Marchantia 

 (PL 32. fig. 35), and other Liverworts. With 

 these are nearly connected the structures 

 called ELATERS, which are found mixed 

 with the spores in the same plants. These 

 are tubular cells containing a single or dou- 

 ble elastic spiral fibre (PI. 32. figs. 36-38), 

 exactly analogous to the spiral vessel in 

 structure. Elaters of similar nature occur 

 even among the Fungi, as in the sporange 

 of TRICHIA (PL 32. figs. 39, 40). The ela- 

 ters of the Equisetaceaj (fig. 209, p. 242) 

 are of different character, consisting of four 

 short filaments with clavate ends, attached 

 at one side of the spore and originally coiled 

 round it, ultimately unrolling with elasticity. 

 They appear to be formed by the deposition 

 of a spiral-fibrous layer on the wall of the 

 parent-cell of the spore, within which the 

 true (single) spore membrane is formed, un- 

 adherent; and when the spore is ripe, the 

 spiral-fibrous layer splits up and starts away 

 from the inner coat. An elegant spiral and 

 annular fibrous structure is also met with in 

 the large cells of the leaves of the SPHAG- 

 NACE.E (PL 39. fig. 25); this is exactly 

 analogous to the similar deposits in the 

 higher plants. Spiral layers are found, less 

 distinctly, in the radical hairs growing from 

 the lower surface of the frond of MARCHAN- 

 TIA. Nageli regards them as folds of an 



inner layer of membrane, but they appear to 

 be regular secondary deposits. 



Lastly, the hairs and similar epidermal 

 appendages sometimes exhibit spiral-fibrous 

 deposits. An unreliable spiral fibre is beauti- 

 fully arranged in the cells forming the mealy 

 coating of the seed of Cobaa scandens (PL 

 21. fig. 20). The seeds of many of the 

 Acanthaceae (PL 2] . figs. 21 & 24), Collomia 

 (PL 21. fig. 22), the pericarp of some of 

 the Labiatae (PL 21. fig. 23), and Composite 

 (SENKCIO) bear tubular hairs, consisting of 

 cells with a spiral or annular fibre in their 

 interior (see HAIRS, of Plants). The struc- 

 ture of the hairs of Collomia, Ruellia, &c. has 

 been much discussed, but it seems very sim- 

 ple ; they appear to consist of a short tubular 

 cell, upon the wall of which a closely coiled 

 elastic spiral-fibrous layer is deposited; 

 during the ripening of the seed the primary 

 membrane undergoes a metamorphosis into 

 a substance related to amyloid (or bassorin?), 

 which softens and swells up when placed in 

 water, allowing the spiral fibre to extend 

 itself (PL 21. figs. 21, 22 b, c). Sulphuric 

 acid and iodine give the swollen gum-like 

 envelope a purplish tint. 



Another and less distinctly marked spiral 

 arrangement of the substance of the cell- 

 walls, occurs in the form of cracks or gaps 

 in certain of the layers of the secondary de- 

 posits, running more or less round the cell, 

 appearing like irregular spiral streaks ; these 

 are sometimes present in the earlier second- 

 ary layers, and not in the later, so that the 

 "cracks" are covered in by the latter, and 

 converted into canals in the substance of the 

 cell-wall. These occur in the wood-cells of 

 Hernandia sonora, in the prosenchymatous 

 cells of the vascular bundles of Caryota 

 urens, Ph&nix, Metroxylon, and probably in 

 other cases. Something similar may be de- 

 tected in the wood-cells of Pinus (PL 39. 

 fig. 1), especially after treatment with boiling 

 nitric acid. In liber-cells a spiral texture is 

 far more generally evident. In Vinca, for 

 instance (PL 39. fig. 30), and other Apocy- 

 naceous plants, a delicate spiral striation of 

 the wall is evident in its natural state, beau- 

 tifully regular in its arrangement ; a similar 

 appearance may often be detected in the 

 walls of thickened hairs, especially when 

 acids are applied, as in Cotton (PL 21. fig. 

 1 b), particularly in gun-cotton (fig. 1 c) ; 

 sometimes with intermediate slits, as in Ur- 

 tica (PL 21. fig. 8), &c. ; and by boiling with 

 nitric acid, a minute spiral-fibrous structure 

 may be detected in the secondary layers of 



