THE GENUS EUCALYPTUS. 223 



years. This same species, however, under less favourable cir- 

 cumstances, is of much slower growth, as I have noticed " blue 

 gums," which, as far as I have been able to judge, have not 

 attained a diameter of two feet in fifty or sixty years. The 

 subject is one of great interest, and opens for consideration 

 questions intimately connected with the geological formation of 

 the colony, and the probable period that may have elapsed since 

 some parts of it were first covered with forests. A careful 

 comparison of observations made in different colonies, with the 

 express view of ascertaining the ages of our gigantic Eucalypti, 

 might lead to the solution of many problems connected with the 

 physical history of the continent, which are now enveloped in 

 obscurity ; but there are great difficulties in the consideration of 

 a question in which so many counteracting influences are in 

 operation. Differences of soil, the prevalence of drought, the 

 ravages of insects, the damages arising from storms, and many 

 other causes of an injurious character, tend to retard the pro- 

 gress of our gums, and to make their growth exceedingly 

 irregular. 



SPECIES OF EUCALYPTUS ARRANGED ACCORDING 

 TO THE CORTICAL SYSTEM; 



A CCOKDINGr to the recent estimate of Mr. Bentham and 

 Dr. F. Mueller, in the third volume of the Flora Australiensis, 

 the number of species belonging to the genus Eucalyptus in Aus- 

 tralia is estimated at 135, of which nearly 50, with numerous 

 varieties are supposed to be indigenous in New South Wales. 

 Future investigations will no doubt suggest many alterations in 

 the arrangement of the species, as probably, in some instances, 

 mere varieties are regarded as distinct species, whilst, on the 

 other hand, some trees, which must always be deemed separate 

 in the eyes of the colonists, have been united together. It is not 



