THE AUSTRALIAN GREY MANGROVE. 257 



between the half wave-length of the gravest vibration 

 and the length (I) of the rod (of uniform section) tends to 

 vanish relatively when the section is reduced without 

 limit." 



The experiments lend no support to Macdonald's calcula- 

 tion which requires that the numbers in the table under the 

 heading ' k observed ' should be 2*5. It would appear, then, 

 that Sarasin and De la Rive's well known experiments 

 which, hitherto, have only been quantitatively described in 

 terms of Macdonald's theory, still await their explanation. 



THE AUSTRALIAN "GREY MANGROVE," 



(Avicennia officinalis, Linn.) 



By R. T. Baker, f.l.s., 



Curator, Technological Museum, Sydney. 



With Plates XXVII -XLVI. 



[Read before the Royal Society of N. 8. Wales, November 3, 1915.'] 



1. Introduction. 



2. Description of Species. 



3. Synonymy. 



4. Systematic position of this Australian Mangrove. 



5. The Leaves. 



6. The Breathing Roots. X^ QlXm ,fl *^4^ 



7. The Seed. Ar n niC 



8. Timber:— (a) Economics. Ify OCT 2"' 



(b) Analysis of the Ash. \ k* « N 



(c) Macroscopical Characters. v^^O/JrI WiV)^" 



(d) Histology. 



(e) Fibres. 



9. Bark. 



10. Concentric "Rings," and their relation to the age of the tree. 



11. Illustrations. 



Q— November 3, 1915. 



