406 Transactions. 



The trunk of this tree is at the present time about 34 cm. in diameter, the 

 actual base being swollen and wider. At 1-8 m. from the ground it oives 

 off four erect branches, and it is at this point that the bunches of rhizomes 

 are situated, though not merely at the forking, but to within 1-25 m. from 

 the base of the tree. Plate XXIX gives a far better idea of the appearance, 

 &c., than any detailed description. The largest bunch of rhizorrrt's is 38 cm. 

 long and 18 cm. deep. These bunches arise from lateral branches being 

 freely produced, and which, through their positive geotropism, are brought 

 close together. A rather large branch measures 18 cm. in length and 17 mm. 

 in diameter. Short rudimentary lateral roots pass off horizontally from 

 their sides. 



Eegarding the cause of this abundant growth of aerial rhizomes I can 

 say nothing. The tree is at present rapidly dying, and the growth may be 

 in the first instance pathological. It is not altogether dependent on the 

 branching of the tree, since some of the rhizomes are given off far below the 

 forking ; others, again, where there is no branching, on one of the primary 

 branches. It is evident, however, that under certain conditions — at present 

 unknown — Cordyline austraUs can put forth from presumably the same 

 tissue either an ordinary leafy ascending shoot or a rhizomatous descending 

 one. 



EXPLANATION OF PLATE XXIX 



Aerial rhizomes growing high up on trunk of Cordyline australis. 



Art. XL. — The Wellington Tide-gauge. 



By C. E. Adams, M.Sc, A.I.A. (Loud.), F.R.A.S. 



[Read before the Wellington Philosophical Society. 1st July. 1908.] 



The Wellington tide-gauge differs materially from all other tide-gauges, and, 

 as its design avoids most of the sources of error in the usual patterns, an 

 account of its great advantages is now submitted ; but in order to appre- 

 ciate these advantages it will be necessary to refer briefly to the essential 

 features of the usual forms. 



In vol. xvi* of the G.T. Survey of India it is stated that " the object 

 aimed at in any complete system of tidal observations is to obtain the height 

 of the tide above some fixed m.ark or datum for every instant of time during 

 a more or less extended period. . . . This object is attained graphic- 

 ally by causing the rise and fall of the water to communicate its motion, 

 by mechanical means, to a pencil which traces a line on paper wound round 

 a drum turned by clockwork once in twenty-four hours. . . . An 

 instrument such as above briefly described is called a self-registering tide- 

 gauge, and of these various forms have from time to time been constructed. 

 The best form is, according to the opinion of Sir William Thomson, one in 

 which the drum is inclined to the vertical, as this enables the friction between 

 the pencil and the paper to be nicely regulated. The pattern almost ex- 



* " Details of Tidal Observations," p. 9. 



