236 SANTALAGEM. 



one or two rows of somewLat irregular cells. On a transverse 

 section, the distance of tlie medullary rays from eacli other is 

 very different. According to the size and j30sition of the 

 vessels^ the medullary rays are somewhat undulated. Most of 

 the vessels are very large, the largest as much as 89 mkm. m 

 diameter. They are very regularly distributed^ either isolated, 

 or in groups of two or three, very seldom more. Their walls 

 are very thick, being marked with numerous annular pits, 

 communicating with those of the surrounding cells. There is 

 also to be met with in the wood, parenchymatous tissue to some 

 extent, which is made up either of isolated cells or of short 

 tangential or oblique rays of two to five cells ; these parenchy- 

 matous layers very seldom run from one medullary ray 

 another. Crystals of oxalate of calcium are also found ; and 

 in longitudinal sections they are seen to be enclosed in long 

 ducts, containing each 10—15 crystals. As to the concentric 

 zones of darker and brighter tint, as mentioned above, the 



to 



vessels of the latter zones are much smaller and less numerous 

 than those of the dark ones ; the librif orm cells likewise show 

 the same diSorence, although less distinctly. Thus the dai 

 zones in all probability represent the wood built up m spriiio- 

 The vessels have an average diameter of 74 mkm., those of the 

 vessels in the other rings being only 47 mkm. 

 - " The darker colour is due partly to the actual cell-walls, partly 

 to the resin contained in numerous vessels. On the whole, 

 concentric max^kings or zones are more distinct to the nakecL e^ 

 than under the microscope. On a vertical section the medullary 

 rays are seen to be built up of usually less than eighteen layers, 

 each consisting of two or three rows of cells. The position o 

 the medullary rays and pits does not allow this wood to be classed 

 among the woods which wore described by Ilohnel as showing 

 the remarkably regular arrangement of layers or series like 

 Btories, which he termed a 'stockwerkahnliche ' structui^e. ^ 

 those slices of the wood are boiled for some minutes with nitric 

 acid (M85), a little chlorate of potassium being added, the 

 single cells arec...ily isolated. The Hbrif orm cells are then 

 distinctly seeu to exhibit the tvpic form alluded to above, a ft-^ 



