PITS 



15 



or Acacia {Rohinia Pseudacdcia), in wliich tlie wood consequently 

 appears non-porous, but, their cell-walls being tliin, tbe tyloses 

 appear in transverse section as ligbt yellow spots on the dark 

 heartwood. In Letterwood {Brosimum Auhletii), on the other 



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.17. 



Fig 10 —Elements of Oak Wood, highly magnified /, fibre , w p, part of rovr of 

 wood-parenchyma cells , tr tracheid , p v, trachea (part of) ; sp, part of a spiral vessel 

 (From The Oak, by permission of Prof Marshall Ward and Messrs Kegan Paul, 

 Trench, Trllbner & Co ) 



hand, the tracheae are filled up with tyloses, the cells of which 

 have their walls very much thickened so that they appear 



vJlcuI. JnL* 



We come next to the tissues which are of the greatest im- 

 portance in our present study — ^those of the x^km or wood, 



