This section is from the book "A Research On The Eucalypts Especially In Regard To Their Essential Oils", by Richard T. Baker, Henry G. Smith. Also available from Amazon: A Research On The Eucalypts And Their Essential Oils.
Eucalyptus species, however, do not all grow to a large size, the "Mallees" more particularly, and, for the reasons mentioned above, this shrubby growth is perhaps more useful for oil distillation than are the bigger species; besides several of the "Mallees" produce excellent cineol oils.
In certain portions of New South Wales, Victoria and South Australia, or, as a matter of fact, Australia generally, a considerable area of the country is covered with this shrubby Eucalyptus growth, which is known in Australia as "Mallee scrub." Several species occur in this "Mallee Belt," such as E. poly-bractea, E. oleosa, E. Morrisii, E. dumosa, E. Behriana, E. viridis, E. cneorifolia, etc, all of which have the form and growth peculiar to the "Mallees," that is several stems springing from one root.* These species are usually found intermixed, some growing in one locality and some in another, but all have the same general appearance.
One of the best of the "Mallee" species, for oil distillation, is E. polybractea, known in Victoria as "Silver leaf Mallee," and in New South Wales as " Blue Mallee." In the Wyalong district of the latter State, as well as in the Inglewood district of Victoria, E. polybractea is extensively exploited for its oil, and much of the richer cineol Eucalyptus oil forwarded to Europe and America during the last few years has been derived from that Eucalypt. In South Australia, at Kangaroo Island, the species employed is E. cneorifolia, chiefly.
In the Wyalong district a considerable area of country is covered with "Mallee," and in some portions E. polybractea is present to the extent of from 40 to 50 per cent. of the total Eucalyptus growth. The material from the older trees of the "Blue Mallee" is not so useful for oil production as the younger growth, one reason being the yield of oil is not so great, and in order to secure an abundance of new leaf various devices have been adopted. One method is to employ a heavy roller and with this crush down the whole of the natural growth of the "Mallee Scrub." When the broken-down material becomes dry enough it is burnt off, all vegetation upon the ground being destroyed in the fire, but in a few weeks the young growth commences to appear in abundance, springing from the buried nodular root masses of the "Mallee," and in twelve to eighteen months is ready to be cut for oil distillation.
The abundance of new growth of the characteristic silvery leaf of this species, after this treatment, makes quite a pretty picture in the landscape, and is quite distinctive from the young growth of the other species.
* Photographs showing this form of growth will be found under E. oleosa, E. polybractea, and other species known as "Mallees."
The following series of photographs will serve to illustrate this method of working the "Mallee Scrub" in the Wyalong district of New South Wales, so that an abundance of new leaf may be produced, and also to free the country from certain objectionable growths common to the "Mallee" in its natural state.
Plate xcv represents the heavy roller and the way the material is broken down in preparation for burning off.
Plate XCVI shows the "face" of the "Mallee" still remaining, and also where the roller has passed along, crushing everything in its path.
Roller used for crashing down the "Mallee" growth prior to burning off.
"Mallee" growth, showing path of the roller and the face of remaining "Mallee."
Plate XCVII, taken twelve months after the fire, shows the foliaceous growth which had taken place, and nearly the whole of the leaf shown in the picture is that of E. polybractea.
Although machinery has not yet been employed to cut and collect this new growth, yet it is thought that such a method of working should not be difficult, and it is proposed to endeavour to devise machinery to do this work, in order to minimise the initial cost of collection.
During the year 1919 large areas of the "Mallee Scrub" in the Wyalong district were being rolled and treated in this way, so that eventually abundant supplies of new leaf should be available there for oil distillation, and as the stills are modern in construction and of fair size, the establishment of an extensive Eucalyptus oil industry in the Wyalong district should be assured.
The chief species of "Mallee" growing in the "Mallee Belt" in the immediate neighbourhood of Wyalong, besides E. polybradea, are E. Behriaka, E. oleosa, and E. viridis. The constitution of the oils, as well as the yields, from these Eucalypts, will be found recorded under the respective species in this work.*
Showing new growth, twelve months after burning off the rolled "Mallee."
The above remarks in reference to E. polybractea and its associated species in New South Wales, are generally applicable to the conditions which obtain in the corresponding "Mallee Belt" in Victoria, where the Eucalyptus oil distilling industry is somewhat extensively carried on, and well established.
* Another plant of common occurrence associated with E. polybradea is the "Broombush," Melaleuca uncinala. The oil of this Melaleuca is, in composition, very similar to that of "Cajuput," so well known in pharmacy, and might well be considered as an Australian "Cajuput." (See Proc. Roy. Soc, N.S.W., December, 1907.)
The accompanying illustration (Plate XCVIII) shows the method for procuring young material for distillation in the Bendigo district of Victoria.
The extension of the wheat areas in the Wyalong district is rapidly encroaching on the "Mallee," and much of it has already been destroyed, the land being utilised for agricultural purposes, and it seems that if portions of this natural vegetation, where the "Blue Mallee" grows most abundantly, are not conserved for the purpose of oil distillation, in a few years little material of E. polybractea will be procurable in the immediate neighbourhood of that town.
Reproduction of young material for oil distillation, Bendigo district, Victoria.
In Kangaroo Island the "Mallee" E. cneorifolia is utilised for oil production to a considerable extent, and in a paper published in 1912 by Mr. H. J. Wiadrowski, an oil distiller on the island, it was shown that E. cneorifolia had, without any attention or cultivation, given a nett return of £3 per acre, and with a little effort to improve the leaf, it would be more profitable to conserve the "Mallee" for oil, than to work the land for grain, as the nett profits per acre would then be greater than from a 20-bushel crop of wheat at 3s. 6d. per bushel. This estimate was made at the time when Eucalyptus oil was very much cheaper than it is to-day.
The illustrations given previously show how readily the oil-producing species renew their foliage, so that providing the necessary areas are conserved for the purpose of Eucalyptus oil production, abundant material for the preparation of certain classes of oils should be assured.
The "Peppermint" species, in the majority of cases, produce phellandrene oils together with piperitone, or cineol-phellandrene oils, and occasionally cineol oils without phellandrene. They grow most abundantly on the mountain ranges, and in country that probably will not be required for agricultural purposes, so that beyond the work needed for concentration in these areas, no further cultivation, with these species, need be considered.
With the perfumery oil-producing species, and to a lesser extent those yielding the richer cineol oils, the case is different, and it seems to us that the time is approaching when it will be necessary for certain species to be cultivated for their oils, if the increasing demands for these products is to be met in a satisfactory manner. Unfortunately the idea of systematically cultivating Australian plants for the production of their economics appears to have little interest for the average Australian, the tendency being rather towards the destruction of the native vegetation. The eventual shortage of supplies seems to have little influence, and this is evidenced in several directions.
So far little has been done in Australia in the direction of cultivation, and consequently accurate data in this connection, particularly with the oil-producing species, are limited.