34 



THE ANATOMY OF WOODY PLANTS 



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and are widespread in leguminous woods. 

 The presence of fibers of this description is 

 often of value from the hygroscopic quality 

 imparted to the wood, which prevents undue 

 shrinking or swelling. Those species of oak 

 with mucilaginous fibers are stated to be of 

 special utility for cabinet work on account of 

 their relative immunity from swelling and 

 shrinking. In the case of the black locust 

 (Robinia Pseudacacia) the numer- 

 ous mucilaginous fibers made the 

 wood particularly valuable for tree- 

 nails in the days of the construc- 

 tion of wooden ships. Obviously a 

 very important property of such a 

 wooden spike is that it shall neither 

 swell unduly in water nor shrink 

 extremely in the sun. 



Another important group of 

 fibers is that included under the 

 head of septate fibers. These occur 

 very commonly in dicotyledonous 

 woods, particularly in shrubby and 

 herbaceous forms and vines belong- 

 ing to widely separated natural 

 orders. In this type the mechani- 

 cal element is divided transversely 

 by more or less delicate partitions 

 of a cellulosic or pectic nature, 

 which on staining with hematoxylin 

 and safranin stand out sharply 

 from the lignified longitudinal walls 



FIG. 27 



FIG. 28 



FIG. 27. Septate fibers from the vine 

 and teak (Tectona grandii). 



FIG. 28. Substitute fiber of the bar- 

 berry. 



