EXEMENTAEY STErCTTJEE. 



41 



generally terminate obliquely {fig. 77), and, when they combine 

 with neighbouring vessels, the obliqxie extremities of the latter 



Fig. lb. 



Fig. 76. 



Fig. 77. 



Figs. 75 and 76. Beaded pitted vessels. Fig. 77. Pitted 



vessel teniiiiiatiiig olili-iuely, and showinij tbat the 

 p.irtition wall by which it was separated from the ad- 

 joining vessel has been iucomplecelj' absorbed. 



are so placed as accurately to correspond -with the former. In 

 some cases, however, where the pitted vessels are pointed at the 

 ends, they overlap more or less by these points {fig. 25). Pitted 

 vessels may be commonly found in the wood of Dicotyledons ; 

 they are mixed here with the ordinary wood-cells, but are much 

 larger than these, 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. 161, v). The pitted vessels are jj^-^, -g y,- ^g 

 generally among the largest occurring in any •^' ' tf- ■ 

 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. 78), or two or more 

 fibres {fig. I'd) running parallel to each 

 other. Those with only one spiral fibre are 

 termed Simple Spiral Vessels; those with 

 more than one, ComjJoicnd Spiral Vessels. 

 The latter kind are well seen in the stem of 

 the Banana and allied plants, in the young 

 shoots of the Asparagxis, and in the Pitcher 

 Plant. The fibre contained within the spiral ^'l\^^^\ Simple spiral 

 vessel is generally so elastic as to admit of Compound spiral ve^' 

 being uncoiled when the vessel is pulled seJ. 

 asunder, in which case the wall is ruptured between the coils. 

 This may be commonly seen by the naked eye by partially 

 breaking the young shoots or leaf-stalks of almost any plant, 



