ELEMENTAET STRUCTURE. 



33 



ends, they overlap more or less by those points {fig. 9). Some- 



Fig. 59. 



Fig. 60. 



Fig. 61. 



Figs. 59 and 60. Beaded pitted vessels Fig. 61. Pitted 



vessel terminating obliquely, and showing that the par- 

 tition wall by wliich it was separated from the adjoining 

 vessel has been incompletely absorbed. 



times pitted vessels present a branched appearance. They may 

 be commonly found in the wood of Dicoty- -p- gg pig 53 

 ledons, and generally only in that part of 

 such plants. They are mixed with the ordi- 

 nary wood-cells, but are much larger than 

 those and the other tissues found there, 

 as may be seen by making a transverse 

 section of the wood of the Oak, Chestnut, 

 and other trees, when the holes then visible 

 to the naked eye are caused by their section 

 {fig. 169, v). The pitted vessels are gene- 

 rally among the largest occurring in any 

 tissue. 



b. Spiral Vessels. — This name is applied 

 to lengthened cylindrical cells with tapering 

 extremities, having either one continuous 

 spiral fibre running from end to end, as is 

 commonly the case {fig. 62), or two or 

 more fibres {fig. 63) running parallel to 

 each other. Those with only one spiral fibre are termed 

 Simple Spiral Vessels; those with more than one, Compound 

 Spiral Vessels. The latter kind are well seen in the stem 

 of the Banana and alhed plants, in the young shoots of 

 the Asparagus, and in the Pitcher Plant, The spiral fibres 

 of Musa textilis, a plant belonging to the same genus as 

 the Banana and Plantain, are used for the manufacture of 

 dehcate muslins in India. The fibre contained within the 

 spiral vessel is generally so elastic as to admit of being un- 



D 



Fig. 62. Simple spi- 

 ral vessels Fig. 



63. Compound spi- 

 ral vessels. 



