VASCULAR TISSUE. _ ‘25. 
pores, but now looked upon as adhering particles. In other 
plants, particularly Coniferae, globules, with a darkness to- 
wards the centre, are found in the sides of the fibre. These - 
are termed glands. Some say that the appearance of glands 
_ is owing to thin spaces in the membrane forming the sides 
of the tubes. 3 Sas 
63. Woody tissue forms a principal part of all tough 
cody parts, as the wood, the bark, the veins of the leaves, 
- It gives strength and tenacity, and also transmits fluids 
through its fibres. 
IIL—VASCULAR TISSUE. 
64. The vascular tissue consists of bundles of tubes or 
vessels. Each tube is formed of one layer or more of mem- 
_, brane ; tapers, and is conical towards its extremity ; and has — 
a fibre developed in a spiral form on its inner surface, or is 
3 marked transversely on its sides by streaks or lines, showing 
_ atendency to a spiral arrangement. The conical extremi- 
ties of the tubes overlap each other ; and it has been conjec- 
tured that at the point where the extremity of a tube meets 
_ another tube, there is a perforation and communication be- 
tween them, The vessels composing the vascular tissue are 
of two kinds—spiral vessels, and ducts. 
65. Sprrat Vessexs, or Tracher. A spiral vessel con- 
sists of a tube of delicate elementary membrane, with a fibre 
coiled spirally within. If a ribbon be wound spirally round 
_ # cane, and the cane be pulled out, the ribbon will then re- 
_ present the form of the fibre in the tube of a spiral vessel. 
_ The membranous side of the tube is exceedingly thin, and 
the fibre may be easily unrolled, the membrane tearing and 
adhering to it, and being hardly perceptible, except perhaps 
at the tapering extremity of the tube, where the distances 
retween the coils of the fibre are greater. _ Baan 
firal_ vessels are found chiefly in the medullary 
| the veins of the leaves, in the flower, seldom in 
