FIBROVASCULAR TISSUES: PARENCHYMA 



55 



polished end of the trunk of an oak. The wood is clearly separated 

 into two regions, a darker central and a pale peripheral. The 

 deeply colored central region of the trunk constitutes the heartwood 

 or duramen. The uncolored zone which surrounds this is the 

 sapwood or alburnum. The dark-hued heartwood is extremely 

 resistant to decay and constitutes the only material properly 

 utilizable for exposed 

 structures. In the 

 case of dicotyledonous 

 trees in general, one 

 frequently notes even 

 with the naked eye a 

 difference in color 

 between the heartwood 

 and the sapwood. 

 Sometimes this impor- 

 tant distinction is not 

 revealed to the eye, 

 but becomes obvious 

 only under microscopic 

 investigation. Fre- 

 quently the sap indi- 

 cates its boundaries in the felled trunk by the discoloration brought 

 about in its tissues either by oxidases or by fungi, or by both 

 agencies united. In conifers, likewise, a distinction between a 

 darker central heartwood and a surrounding pale-hued sapwood 

 can be often recognized by the naked eye. The redwood or 

 red cedar presents the contrast in color in a very marked manner. 

 The larch and the spruce, which in the microscopic organization 

 of their woods are practically identical, can be readily distinguished 

 from one another by the gross aspect of their trunks. The larch 

 has a dark-brown heartwood, while in the species of spruce the 

 central region of the woody cylinder is in no way contrasted in 

 color with the peripheral sapwood. 



It will be convenient in connection with the discussion of the 

 parenchymatous or storage elements of the wood to elucidate 

 certain features of the microscopic organization of the heartwood 



FIG. 41. Transverse view of an oak log showing 

 heart- and sapwood. 



