PLATE VII (continued) 



Fig. 2. X-ray diagram of wood of Jiiniperus 

 virginiana, beam perpendicular to grain. Note 

 tiie lateral arcs are more intense towards tlieir 

 ends, as predicted by the theory of the spiral 

 diagram. Note also the overlap along the 

 meridian to give spurious meridional arcs. 



Fig. 3. X-ray diagram of a sample of Pinus 

 sylvestris, late wood, 4th annual ring. The 

 lateral arcs are barely intensified at their ends, 

 indicating a wide dispersion of spiral angle in 

 the specimen. The spurious meridional arc is 

 prominent. 





[Facing p. 129 



Fig. 4. X-ray diagram of a sample of Abies sp., 

 10th annual ring, late wood. Note the lateral 

 arcs are rather short and there is no overlap 

 along the meridian. 



The photographs, figs. 2, 3 and 4 similarly demonstrate, therefore, the 



association between the appearance of a meridional arc and the 



tangential spread of the lateral arcs. 



