FUNDAMENTAL OEGANS. 



12? 



space. The dot is placed in the centre of each cup (and corresponds to a thinned 

 portion resulting from the absence of the inner membranes) ; from this thin portion 



there proceeds, on the convexity of each cup, a short 



canal, with only one opening, which leads into the 



interior of the fibre. The lens-shaped cavity arising from. 



the contact of two fibres is usually filled with resin 



(turpentine), which infiltrates into the cavity of the fibres 



and destroys them by degrees; the result is those 



resinous deposits which are often found 



occupying large cavities in the wood of 



conifers (fig. 689, la). 



r.rr. 



Pt- 



J — 



689. Pine. 

 Horizontal slice allowing the deTelopment of two woody 

 bundles in a three-year-old branch (mag.). 



688. Pine. 

 Vertical section of the stem (mag.), p. f, 687. Pine, 



fibre wall ; c. 1, lenticular cavity ; r. m, Punctate fibre 

 medullary ray ; c. f, cavity in a fibre. (mag.). 



Stems of Monocotyledons. — When the monocotyledonous embryo, which is entirely 

 cellular before germination, begins to elongate, fibro-vascular bundles form in its 



stem. These are at first arranged in a 

 ring as in young dicotyledons ; but 

 soon, as the leaves develop, the bundles 

 multiply without any apparent order 

 in the cellular tissue, becoming more 

 numerous and close as they approach 

 the circumference of the stem. If a 

 fully developed bundle be examined 

 under the microscope (fig. 690), it is 

 found to be structurally identical with 

 that of a dicotyledon ; beginning from the central pith, we 

 find walled fibres analogous to liber (l), then trachese (t), 

 then, mixed with cells (p), some of which elongate and thicken 

 into fibres, are seen the openings of rayed or dotted vessels 

 (v) : the circumference of the bundle is formed of thick- 

 walled fibres {liber, l), outside of and amongst which the 

 laticiferous vessels ramify (v.l). 



But, though individual bundles resemble those of a first 

 year's dicotyledonous stem, when taken all together they pre- 

 sent a very important difference (fig. 691), in not being grouped in concentric zones but 



691. Palm. 

 Horizontal slice of the stem. 



T..„. 



690.. Transverse section of a fibro- 

 Tascular bundle of a monocoty- 

 ledonous stem (mag,). ■ (The part 

 answering to the centre of the 

 stem is lowest.) 



