THE AUSTRALIAN GREY MANGROVE. 273 



of a "ring" only. In such a case, it seems to me hardly 

 correct to call them medullary rays, for they do not come 

 from the middle of the stem. The phloem of the broken cell 

 contents is as conspicuous as in other sections. 



Fibres. — These are distinctly seen in the various sections 

 shown, and microscopically examined are found to belong to 

 the simple variety, the walls being relatively thick, and 

 in the lumen are seen oblique slits. The length is over 

 1 mm., and these make up 30 per cent, of the wood by 

 nitric acid method. 



Results of these Histological Investigations 



(a) Practically no true medullary rays, as obtain in 

 secondary wood of dicotyledons, are found in the structure, 

 for what must certainly be classed as "rays" yet are not 

 medullary, as they do not extend from the middle to the 

 outer cortex, being quite restricted in their length to the 

 width of each "ring." 



(b) Bands of vertical walls of sclerenchymatous cells 

 of the round or polygonal or short variety limit the 

 length of the rays,— a feature quite absent in any timber 

 as far as I have been able to ascertain. 



(c) The phloem cells in regular clusters on the outer 

 edge of each ring, appear to perform the function of 

 ordinary exterior bark, as shown when the tree is ring- 

 barked. 



(d) The remarkable disposition of the wood fibres. 



(e) The work of cambium being performed apparently by 

 the wood parenchyma between the wood fibres and the 

 stone cells. 



(f.) There is nothing in the wood which corresponds with 

 the spring and autumn growths of other dicotyledonous 

 trees. 



E— November 3, 1915. 



