48 ON THE PLANT-CELL. 



takes place in the old stems of Scitammete, and of speces of Commelinece, 

 as in Hedychium Gardnerianum, and Tradescantia crassula. Another 

 regular formation of anastomosing fibres occurs between the spires of 

 neighbouring cells. This may be seen in the large knotted vessels of 

 many Balsaminece. In these may be seen a perfectly regular spiral fibre 

 with a slight yellow colouring, but accompanied by another short, almost 

 colourless, vertical branch, which is easily recognised by its transparency. 

 If this is traced it will be found to follow accurately the course of the 

 commissure between the two vessels, and to form a kind of bridge over 

 the commissure from one fibre to another. This clearly does not belong 

 to the original spiral formation. Its constant appearance in porous 

 vessels, with long transverse clefts, has caused it to be called scalariform 

 tissue. 



In the last place the annular ducts present some striking phenomena, 

 amongst which must be reckoned the constancy of the distance between 

 the same annuli. A remarkable instance of this I have observed in 

 Canna occidentalis, where a short distance between the annuli regularly 

 alternates with one three times as long (fig. 31. .). In the annular ducts 

 of the petioles of Musa paradisiaca, I have observed the cell between 

 the two rings to be remarkably distended and swollen, so that there could 

 be no union with the rings of cells near to each other. 



Historical and Critical Remarks. The spiral fibres were early dis- 

 covered by Malpighi and Grew, or perhaps even sooner by Henshaw. 

 Bernhardi (Ueber Pflanzengefiisse und cine neue Art desselben : Erfurt, 

 1805) and Moldenhauer (Beitrage zur Pflanzenanatomie : Kiel, 1822) 

 pointed out the existence of the external cell-membrane enveloping the 

 spiral fibre. The annuli or rings were discovered by Bahel, and their 

 enveloping membrane by Bernhardi. (See Link, Elementa Philosophise 

 Botanies, ed. sec. torn. i. p. 27. 169.) The porous cells were discovered 

 by Leuwenhoek (Opera omnia, tab. 462. fig. 20.); but they were first 

 correctly estimated by Mirbel (Histoire Nat. des Plantes, 1800, torn. i. 

 p. 57. ; Traite d' Anatomic et de Physiol. veget., Paris, 1802, t. i. p. 57. 

 fig. 1 4.). He was at first opposed till Hugo Mohl published his ob- 

 servations confirming Mirbel's views (Ueber den Bau der Ranken und 

 Schlingpflanzen, Tub. 1828). Mohl also discovered the membrane in- 

 vesting the porous cells (Ueber die Poren des Pflanzenzellgewebes, Tub. 

 1828). These are the most important steps in the history of our know- 

 ledge. What remains is the notice of the more or less frequent occurrence 

 of one or another modification. Meyen (Physiologic, vol. i.) has collected 

 a large mass of information on the whole of this subject. Valentin (Re- 

 pertorium, vol. i.) was the first to contend that all these formations origi- 

 nate in the spiral. Link (Elementa) maintains that the pores and clefts 

 are portions of torn spiral fibres. Mohl is of opinion that the annular 

 ducts are primary formations. Hartig (Beitrage zur Entwickelungsge- 

 schichte der Pflanzen, &c. Berlin, 1848) has announced a view of spiral 

 cell development which cannot be regarded as any thing more than an 

 ingenious fiction, it having no foundation in facts. 



19. Generally, the deposit-process forms a new layer on the 

 wall of the cell of the same form ; but cases occur in which on the 

 one side of the wall it unites a spiral fibre to a homogeneous mem- 

 brane, whilst on the other it excavates a spot for a fissured pore 



