SPIRAL STRUCTURES, [ 713 ] SPIRAL STRUCTURES. 



the wall is covered with a continuous layer. 

 A similar structure, generally with perfect 

 spiral fibres, occurs in the walls of the spo- 

 ranges ofjunycrmminia, Marchantia (PL 40. 

 fig. 35), and other Liverworts. With these j 

 are nearly connected the structures called i 

 ELATERS, which are found mixed with the I 

 spores in the same plants. These are tu- 

 bular cells containing a single or double 

 elastic spiral fibre (PI. 40. 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 THICHIA (PI. 40. figs. 39, 40). The ela- 

 ters of the Equisetaceee (fig. 205, p. 300) 

 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-men- 

 brane is formed, unadherent ; 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 struc- 

 ture is also met with in the large cells of the 

 leaves of the SPHAGNACEJE (PL 48. fig. 25) ; 

 this is exactly analogous to the similar de- 

 posits in the higher plants. Spiral layers 

 are found, less distinctly, in the radical 

 hairs growing from the lower surface of the 

 frond of MARCHANTIA. Nageli regards 

 them as folds of an inner layer of mem- 

 brane ; but they appear to be regular secon- 

 dary deposits. 



Lastly, the hairs and similar epidermal 

 appendages sometimes exhibit spiral -fibrous 

 deposits. An unreliable spiral fibre is 

 beautifully arranged in the cells forming 

 the mealy coating of the seed of Cobeea 

 scandens (PL 28. fig. 20). The seeds of many 

 of the Acanthacese (figs. 21 & 24), Collomia 

 (fig. 22), the pericarp of some of the Labiatae 

 (fig. 23) and CompositaB (SENECIO) bear 

 tubular hairs, consisting of cells with a spiral 

 or annular fibre in their interior (see HAIRS 

 of Plants). The structure of the hairs of 

 Collomia, Ruellia, &c. has been much dis- 

 cussed, but it seems very simple : they ap- 

 pear 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 bassorine ?), which 

 softens and swells up when placed in water, 



allowing the spiral fibre to extend itself (PL 

 28. tigs. 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 

 deposits, running more or less round the 

 cell, appearing like irregular spiral streaks ; 

 these are sometimes present in the earlier 

 secondary layers and not in the later, so 

 that the " cracks " are covered in by the 

 latter and converted into canals in the sub- 

 stance of the cell -wall. These occur in the 

 wood-cells of Hernandia sonora, in the pros- 

 enchymatous cells of the vascular bundles 

 of Caryota urens, Phoenix, Metroxylon, and 

 probably in other cases. Something similar 

 may be detected in the wood-cells of Finns 

 (PL 48. 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 48. fig. 30), and 

 other Apocynaceous plants, a delicate spiral 

 striation of the wall is evident in its natural 

 state, beautifully regular in its arrange- 

 ment ; a similar 'appearance may often be 

 detected in the walls of thickened hairs, 

 especially when acids are applied, as in 

 Cotton (PL 28. fig. 1 b), particularly in gun- 

 cotton (fig. 1 c) sometimes with interme- 

 diate slits, as in Urtica (fig. 8), &c. ; and 

 by boiling with nitric acid, a minute spiral- 

 fibrous structure may be detected in the 

 secondary layers of the liber-cells of very 

 many plants, as of Flax (fig. 2 b, c), Coir 

 (fig. 5 a, b), Bcehmeria (fig. 25 b, c), &c. 

 All these spiral structures belong to the 

 secondary deposits of the cells ; they are 

 mostly distinguishable from those previously 

 described by being thinner places or lines 

 left bare, instead of being lines of deposit. 



We have observed a somewhat similar 

 spiral streaking of the walls of Hydrodictyon, 

 depending on slits in certain of the laminae. 

 Some of the genera of Oscillatoriaceap, as 

 Ainactis (PL 8. fig. 15 b) and Schizosiphon 

 (fig. 13 d, e), also present a spiral-fibrous de- 

 composition of their cellulose coats when 

 old ; and we have seen a spiral marking on 

 the wall of Cladophora, as described by 

 Mitscherlich. Agardh has stated that he 

 detected a complicated spiral-fibrous struc- 

 ture in the cell-wall of Confervas, extending, 

 however, from one cell to another ; and he 

 regards this as a proof of the spiral structure 

 of primary cell-membrane generally; and 



