SPIRAL STRUCTURES. 



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SPIRAL STRUCTURES. 



the liber-cells of very many plants, as of 

 Flax (PL 21. fig. 2 b, c), Coir (PI. 21. fig. 

 5 a, b), Boehmeria (PI. 21. fig. 2 b, c), &c. 

 All these spiral structures belong to the se- 

 condary deposits of the cells ; they are mostly 

 distinguishable from those previously de- 

 scribed 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 laminse. 

 Some of the genera of Oscillatoriaceee, as 

 Ainactis (PL 4. fig. 15 b) and SchizosipJion 

 (PL 4. fig. 13, d, e), also present a spiral- 

 fibrous decomposition of their cellulose coats 

 when old ; and we have seen a spiral mark- 

 ing on the wall of Cladopliora, as described 

 by Mitscherlich. Agardli has recently stated 

 that he detected a complicated spiral-fibrous 

 structure in the cell-wall of Confervae, ex- 

 tending, however, from one cell to another ; 

 and he regards this as a proof of the spiral 

 structure of primary cell-membrane gene- 

 rally ; and he says he has likewise detected 

 an analogous spiral-fibrous structure in the 

 primary cell-wall of the structures of the 

 Phanerogamia. With regard to the fibrillous 

 structure of the walls of the Confervoids, 

 this appears comparable with that we have 

 described in the liber-cells, especially of 

 Vinca ; and apparently a delicate spiral struc- 

 ture of this kind exists in all cell-membranes 

 which have received thickening layers ; but 

 in reference to the coarse interlaced fibrils 

 figured by Agardh, we believe there is an 

 error of observation. If cells of the fruit of 

 the white snow-berry {Symphoricarjms) are 

 allowed to dry upon a slider, they fall into 

 minute creases, often running spirally; if 

 boiled in nitric acid, they are cleared of ad- 

 hering protoplasm, &c., and minute creases 

 or folds of the same kind are produced in 

 greater abundance ; but a very careful exa- 

 mination and observation of the ends of the 

 folds, their nregular directions, &c., and 

 especially when coloured with iodine, has 

 convinced us that in this case no real spiral 

 structure exists, although at first sight the 

 appearance is very deceptive. These fine 

 folds must not be confounded with the deli- 

 cate striation above alluded to. As to this 

 striation, however, existing as it does so ge- 

 nerally, it raises an interesting question as 

 to whether the secondary membranes are 

 always composed of delicate fibrils. Criiger 

 asserts that they are, and declares that he 

 has resolved every form of secondary deposit 

 into primitive fibrils, in liber-cells, wood- 



cells, parenchymatous cells, pitted cells, and 

 also the large fibres of the spiral vessels, &c., 

 the broken ends of which he represents as 

 split up into a kind of brush of fibrils ; these 

 however cannot be isolated so as to trace 

 their com'se ; and the most we can say is, 

 that the membrane often tears most readily 

 in the direction of the striae ; and in some 

 liber-cells, moreover, the secondary deposits 

 tear readily into perpendicular fii3rils after 

 maceration (PL 21. fig. 26 c). The delicate 

 striation of the membranes of the Confervse 

 and slightly thickened liber- or parenchy- 

 ma-cells of many Flowering plants, form 

 a desirable object of investigation for those 

 accustomed to the delicate observation of 

 the markings of the valves of the Diatoma- 

 ceae. The use of reagents, such as nitric 

 acid and solution of potash, boiling, ma- 

 ceration, and other means must be employed 

 for this purpose, controlled always by a care- 

 ful observation of the structures in their 

 natural state and in difi'erent stages of de- 

 velopment. It is not impossible that all 

 secondary deposits may prove, as Meyen 

 assumed, to have a fibrous constitution, and 

 true membrane to be confined to the primary 

 walls. One set of layers, however, seem 

 always to resist the endeavour to resolve 

 them into fibrils, namely those of the horny 

 and fleshy Albumen of seeds. 



As to the mode of the formation of spiral 

 secondar)^ deposits, little is certainly known 

 at present. Criiger attributes them to spiral 

 circulation of the secreting protoplasm over 

 the cell-wall in the position of the future 

 fibres. We believe this to be a somewhat spe- 

 culative notion. Others have asserted that 

 they are formed by gradual collocation of 

 visible grjmules ; this is certainly an error. 

 We have observed the gradual formation of 

 the spiral band in the elater oi Marchantia, 

 where it is at first a faint si^iral trace with 

 indistinct edges; as it grows thicker, the 

 edges become more and more defined, and it 

 is produced originally in the exact position 

 and pattern which it subsequently retains. 

 Trecul has lately published an elaborate me- 

 moir, reviving an old notion that the spiral 

 and other fibrous markings are folds of mem- 

 brane thrown inwards from the cell-wall. We 

 believe this to be altogether a misconception. 



The actively moving spiral filaments or 

 Spermatozoids of the Ferns, Mosses, 

 Characese, &c., have nothing in common, 

 except the spiral form, with the structures 

 described in this article ; they belong to the 

 protoplasmic structm*es or cell-contents, as 



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