THE VICTORIAN NATUKALIST. 175 



of flow, and sometimes cutting across transversely. The pheno- 

 crysts, or larger crystals, in this rock are Olivine and Labra- 

 dorite. The Olivine is the ferriferous variety, and shows a 

 tendency to develop a clean brachy-diagonal cleavage. There 

 are no traces of decomposition in the Olivine, but minute 

 crystals of Specular Iron (Haematite) occur as inclusions. Some 

 of the Olivine crystals scattered through the ground-mass are 

 much smaller, and may represent a second crop of the mineral. 

 The phenocryst of Labradorite contains a nuclear mass of 

 included impurities. 



Sample 2. — A vesicular Basalt, having a ground-mass similar to 

 the above, but masked by the ferruginous decomposition products 

 of the Olivine and Magnetite. The phenocrysts of Olivine are 

 very much fractured and cleaved, and are generally in an 

 advanced state of alteration. Some of the less altered Olivines 

 show something akin to Chrysotile structure, the fibres starting 

 from a cleavage surface, and frequently situated at the centre of 

 the crystal. On account of the high percentage of iron in its 

 composition the decomposition product of the Olivine is largely 

 limonitic. — Fredk. Chapman. 



NOTES ON THE MAINTENANCE OF EQUILIBRIUM 

 AND SYMMETRY IN TREES. 

 By H. H. Baker. 

 {Read before the Field Naturalists' Club of Victoria, I2th Dec, 1904.) 

 My attention was directed to this subject by noticing in the case 

 of several trees which had been denuded of branches by storm, 

 and were thus thrown out of balance, that an effort was 

 apparently made on their part to put forth new branches upon 

 the side where the loss had occurred, with the intention of 

 restoring the equilibrium necessary for vigorous growth. The 

 idea presented itself that certain natural causes would probably 

 account for the action of the trees, and I venture to submit the 

 following as an explanation of what has occurred in these and in 

 similar cases. 



One of the most familiar facts in connection with trees is the 

 symmetry and balance which are displayed in their growth, and 

 that, almost without exception, provision has been made to 

 preserve the equilibrium of the plant, so that the centre of gravity 

 is to be found, under normal circumstances, somewhere near a 

 vertical line drawn through the spot from which the centre of the 

 main stem issues from the ground. This can be accounted for 

 largely by the regular manner in which the branches are developed 

 in the axils of the leaves on the young stems. But as the plant 

 advances in age many of these promising shoots disappear, being 

 torn off by storm, withered by want of light or water, or eaten 

 back by insects. 



