STRUCTURE.] FIBRE ALONE. 55 



arches of which remain after the destruction of the roof and 

 walls. According to the observations of Schleiden, the for- 

 mation of fibre never takes place independently of membrane, 

 but occurs in the interior of cells, whose membrane was 

 originally quite simple. He regards Corda's statements to 

 the contrary (Ueber SpiralfaserzeUen, 7 and 8), as formed 

 upon imperfect observations. He says that cells always attain 

 their full size before the fibre appears, and he regards its for- 

 mation as a part of the process of lignification. In the begin- 

 ning he states that each cell is filled with starch, rarely with 

 mucus or gum. By degrees the starch is always converted 

 into the latter ; this becomes changed, and, as it would seem, 

 always from without inwards, into jelly. This jelly changes 

 at its surface into a spiral fibre of variable width, which either 

 does or does not adhere to the sides of the cells, and which 

 may be supposed to owe its spiral direction to the course 

 taken by a current setting between the side of the cell and 

 the central mass of jelly. This seems to be shown by Col- 

 lomia linearis described below, in which the mucus is not 

 precipitated in the form of an inclosing membrane, and by 

 the cu rious hairs of Acanthads, our knowledge of which is due 

 to Mr. Kippist. In these plants various conditions occur 

 between a tubular cell without spiral, and a spiral thread with- 

 out apparent tube. In Blechum Brownei, Ruellia littoralis, 

 &c., will be found tubes without spiral, but discharging mucus 

 through a hole in their end; in Ruellia formosa, a slight 

 appearance of spiral makes its appearance in a mucus tube ; 

 in some Hygrophilas the spirals are broken, or at least appear 

 within tubes in the form of rings, and in Acanthodium, 

 where the spiral acquires a high development, the cell-mem- 

 brane is hardly discoverable. 



The following are the more important varieties : 

 1. Spiral fibres repressed by mucus, but having sufficient 

 elasticity to uncoil when the mucus is dissolved, and 

 then breaking up into rings. (Plate I. fig. 16.) These 

 are what are found in the seed-coat of Collomia linearis. 

 They approach spiral vessels so very nearly, that when I 

 originally discovered them I mistook them for such. 

 They are known by their depressed figure when at rest, 



