18 



INTRODUCTION. 



not confined to the wood, but forms part of the bark, the veins of leaves, 

 &c. In coniferous trees, the fibres or tubes are not only larger than in 



Fig. 2. 



Bundle of Woody Fibre. 



Fig. 3. 



© 



Woody Fibre of Pine. 



Fig. 4. 



Section of Dotted Duct. 



Vascular Tissue 



Fig. 5. 



other plants, but are also marked on their sides with circular dots or disks, 

 the true office of which is not fully understood. 



Vasiform Tissue consists of large tubes which are formed of cylindrical 

 cells placed end to end, and opening into each other ; 

 the sides are marked with dots or pits. They have 

 been termed dotted ducts, and were thought to be true 

 vessels ; these dots are caused by the unequal deposit 

 of solid matter on their interior. They are the largest 

 tubes in plants, and their orifices are conspicuous on the 

 cross section of most kinds of wood, 

 consists of membranous tubes marked with transverse 

 pijr R rings, or with a spiral fibre attached to their 



interior surface. This spiral fibre is the real 

 type of the vascular tissue ; the thin and deli- 

 cate membrane covering the fibre being trans- 

 parent the latter only is visible, and resembles 

 a coil of slender wire. The spiral fibre is 

 usually single, but is sometimes double, or 

 even triple or quadruple. In their perfect 

 state they contain air only. They may readi- 

 ly be seen in their unrolled form, by breaking 

 almost any leafstalk, and pulling the extremi- 

 ties gently asunder. In plants having pith, 

 they are found in a circle around it. 



Where the spiral fibre cannot be unrolled, 

 the vessels are called ducts. Sometimes the 

 turns of the coil are in contact, forming closed 

 ducts, which so closely resemble spiral vessels 

 as only to be distinguished from them, by their 

 not being capable of being unrolled. There 

 are qthers in which the turns are distant, or 

 broken into separate rings placed at regular 

 intervals ; these are called annular ducts. 

 Sometimes the coil terminates in a ring, and 

 then commences again, with the intervention of two or three rings. Some- 

 times they cross each other, when they are termed reticulated ducts, or are 

 broken into short, irregular bands. In some ducts again, no traces of spiral 

 fibre are to be seen. Ducts of all these kinds occur abundantly in the woody 

 tissue of most plants. 



Lactiferous Tissue consists of a series of branching vessels, which freely 



Spiral Vessels. 

 a Single, b Quad- 

 ruple. 



a Annular 

 duct, b Spiro- 

 annularduct. 



