86 



THE ANATOMY OF WOODY PLANTS 



It will be advantageous as a sequel to the representation of the 

 prominent types of rays in the dicotyledons in diagram to view 

 them in actual photographs in the case of the genus Casuarina. We 

 may profitably begin here, as in the case of the diagrams, with 

 transverse sections. Fig. 65 reproduces the cross-section of a 

 small twig of Casuarina Fraseri. The leaves are in the main still 

 present in depressions on the surface of the stem and clearly sub- 

 tend the foliar 

 rays. Rather nar- 

 row leaf gaps pene- 

 tra te the firs t 

 annual ring and 

 are twice as numer- 

 ous as the append- 

 ages at a given 

 node (that is, there 

 are twelve gaps, 

 although only six 

 appendages) . 

 This duplication 

 of the gaps is due 

 to the fact that the 

 whorls of leaves 

 alternate at differ- 

 ent nodes, and the 

 gaps correspond- 

 ing to these are persistent, with the natural result of gaps twice 

 as numerous as the appendages. Fig. 66 shows part of the 

 foregoing much more highly magnified. At the top is a persistent 

 leaf and in the middle line below lies the pith, which is sending off 

 an extension, the leaf gap; and this, on reaching the second annual 

 ring, undergoes considerable enlargement. Between the wide 

 termination of the leaf gap in the beginning of the second annual 

 ring and in line with and subtending the leaf on the outside of the 

 stem lies the foliar ray. The magnification is not sufficient in the 

 figure to show the organization of the leaf ray; hence a more 

 enlarged representation is introduced in Fig. 67. Here it is clear 



FIG. 66. Part of transverse section of a twig of 

 Casuarina Fraseri more highly magnified. 



