113 



elongated, rectangular cells, of considerable consistence, bnt without chloro- 

 phyll, or other colouring matter. 



No stomata or other openings are found on either surface, and the gum 

 appears to be exuded by exosmosis. 



The (ibro-vascular bundles, which form what are commonly called the 

 fibres of the plant, are composed of elongated tubular liber-cells, enclosing a 

 centre of spiral vessels, and vary much in shape in different parts of the leaf. 

 They are surrounded by a layer of elongated cells, that at once turn blue with 

 iodine, and are probably cambium cells. The bundles are thickest at the base, 

 and taper gradually to the point of the leaf. 



The spiral vessels are about 0*001 inch in diameter, and contain a single, 

 rarely a double, spiral fibre, which can be unrolled with a needle. They are 

 filled with air, and have no strength, but are readily broken across. 



The liber-cells, on the contrary, have great strength, and form the true 

 fibre of the leaf. They are very long, probably an inch or more, while their 

 thickness never exceeds 0-0006 inch, and is sometimes only 0-0003 inch.* 

 They taper each way to a more or less blunt point (Fig. III.), each cell being 

 distinct from the rest, and not joined together end-ways. Notwithstanding 

 their strength they are of very delicate structure, colourless, translucent, and 

 almost devoid of secondaxy deposits, the cell-wall being from 0-0001 inch, to 

 0-0002 inch, thick. They are hollow, and filled only with air, but are highly 

 hygroscopic, imbibing water quickly, and during the operation twisting about 

 in all directions. The fibres, although round when separated, are not so when 

 collected into bundles (Fig. XL), being then compressed into ovals, polygons, 

 etc., so as to fill up the whole space, and leave no interstices. They have the 

 same thickness in all parts of the leaf. 



At the base of the leaf the vascular bundles are scattered through the 

 cellular tissue, in about four irregular rows. They are arranged in ovals of 

 two sizes ; the largest, whose major axis is about - 02 inch, and minor axis 

 0-014 inch, enclose, in their centres, a rhomboidal cluster of spiral vessels 

 (Fig. X. s. v.) ; while the smaller, whose major axis is 0-015 inch, and minor 

 axis 0-007 inch, contain none. Near the outer surface of the leaf four other 

 irregular rows of fibre bundles, without spiral vessels, are found, whose section 

 is lanceolate, thus making eight rows altogether in the base of the leaf. The 

 fibres here are generally muclr weaker than in any other part, and can be 

 easily torn across with a needle. 



Near the outside of the leaf the cellular tissue, in which these bundles are 

 imbedded, is lax and translucent, but towards the interior it is open and 

 spongy, the cells being arranged in single rows, enclosing irregular inter- 

 cellular spaces (Fig. X.h.), which are of a tubular form, the tubes running 

 parallel with the vascular bundles. These inter-cellular passages begin to be 

 developed when the leaf is about four inches long, and they are found only in 

 those parts where gum is exuded. At present I have always found them 

 empty, but it is possible that they may be gum-canals, or the glands or ducts by 

 which gum is secreted. 



In the thick part of the butt of the leaf, the internal rows of bundles are 

 reduced to one, the others having died out. (Fig. IV.) They are here club- 

 shaped, with a constriction in the middle (Fig. V.a.), and enclose a rhomboidal 

 bundle of spiral-vessels (Fig. V. s.v.). Besides these there is also a marginal 

 row of bundles, the largest of which (Fig. V.b.) alternate with the bundles of 

 the interior row. They are of an elongated clavate form, constricted in the 



*What are called the cotton-like, or hair-like, filaments of the flax, are far from, 

 being the ultimate fibres, but are single bundles containing perhaps 100 or more liber- 

 cells ; the ultimate fibres are all but invisible to the unassisted eye. 



