FIBROVASCULAR TISSUES: RAYS 



parenchyma and the exclusion of vessels can be readily seen. At 

 b' is indicated the tangential projection of the diffuse condition 

 of rays. Here the original cluster has become scattered and 

 vessels are now present among the rays. In c' is shown the longi- 

 tudinal tangential aspect of the compound ray -that is, the con- 

 dition in which the original aggregation has become fused into a 

 large solid mass of radial parenchyma. 



The conditions 

 in a diagram of a 

 coniferous stem in 

 three dimensions 

 may now be dis- 

 cussed. Fig. 64 

 illustrates the 

 topography of a 

 two-year-old twig 

 of Picea canaden- 

 sis. In the trans- 

 verse aspect the 

 pith surrounded 

 by xylem, phloem, 

 and cortex can be 

 distinguished. 

 Projecting from 

 the surface are the 

 leaves or their bases. The outline of the pith is indented by a num- 

 ber of bays, which are the deeper the nearer they are in the vertical 

 plane to the departing trace of a leaf. In relation to one of these on 

 the side of the pith nearer the observer is an actual trace running 

 horizontally in the wood. The transverse aspect of the wood 

 shows the presence of numerous narrow rays. The face of the 

 stem facing the observer is cut away to show the topographical 

 relations of the leaf traces in the wood. It is clear that, contrary 

 to the conditions observed in the stem of Casuarina diagrammati- 

 cally represented in Fig. 62, there are no modifications in the 

 grouping of the rays or in other features with reference to the 

 foliar traces (appearing as oval dots). 



FIG. 65. Transverse section of a twig of Casuarina Fraseri 



