ANNUAL RINGS 



679 



annual rings. In most Gymnosperms, the bordered pits (which are 

 ordinarily confined to the radial walls of the tracheides) appear on the 

 tangential walls as well, at the limits of each annual ring (Fig. 282); 

 in Pinus, where these tangential pits are absent, the tracheidal elements 



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Fig. 281. 



Part of a T.S. through the secondary xylem and phloem of a twelve-year-old branch 

 of Cylisus Laburnum (at the end of October). />, conducting parenchyma ; b, plate of 

 fibrous tissue ; I, leptome (the larger cells are the sieve-tubes) ; c, cambium ; I/, wood- 

 fibres ; m, mestome (including intermediate cells, xylem-parenchyma, tracheides 

 and narrow vessels) ; g, boundary between autumn and spring wood; m, medullary 

 ray. 



of the xylem-rays are responsible for the radial conduction of water. 

 Among Dicotyledons, according to Gnentzsch and Strasburger, the 

 water-conducting elements of adjoining rays are often connected with 

 one another by means of isolated narrow vessels, which develop in the 



