Dear Mr. MacDonald. —
In reply to your letter received yesterday1 let me advise you to search for the cause of the destruction of groups of trees in your forest region at their roots. You may possibly find that the disease proceeds originally from decayed logs or stumps. If so you will see a filmy mycelium of a fungus cobweb-like enveloping the roots. You may be almost sure that this mycelium is spun out by the agaricus melleus, a mushroom not dis-similar to the common agaricus campestris, which we eat, but its hood is of honey yellow tinge and it often grows in crowds, as the individual plants are connected by a webby mycelium along or beneath the surface of the soil or over the bark of trees, if they are decaying. One of the best means of destroying this dangerous mushroom and its mycelium is the application of boiling water, to which some soap may be added, to the soil. While the hot water penetrates the soil the temperature is yet sufficient to destroy the subtle mycelium threads, but has cooled sufficiently so as not to injure healthy roots of trees. If the disease among your trees, as I suspect and as I have here first pointed out in forest regions, proceeds from agaricus melleus,2 then other fungicides could also be recommended. But the boiling water is simply applied, whereas many other applications would leave noxious substances in the ground. You could anyhow draw through your report, or through the local newspapers, attention to this danger, from the honey-colored mushroom, not only to our forests but to our orchards, more especially so as the agaricus melleus has for many years been known to exist in Australasia and New South Wales as part of it. I should like this to be made publicly known, as this agaricus melleus looks so innocent a thing and would hardly be suspected to do such extensive and insiduous mischief. Other causes, however, may have produced the deadly effect on your trees, such for instance as insects, which may have been parasitically active. Decay of roots may also have been caused by stagnant water at the roots, and extreme dryness in a very hot season may have fissurated the bark, not to speak of other possibilities.
With regardful remembrances,
Yours,
FRS VON MUELLER.
Oct. 25th, 1895.
Agaricus campestris
Agaricus melleus
Letter not found.
For further information, see M to the Editor, Age (Melbourne), 15 November 1895, and notes thereto.
Letter not found. The text given here is from 'Disease in our Forest and Orchard Trees', Macleay argus, 20 November 1895, p. 3 (B95.11.08). It is introduced by a letter from MacDonald to the editor beginning: 'As requested by Baron F. Von Mueller, allow me to draw your attention to his letter respecting the agaricus melleus or honey-colored mushroom, as it is possible that the phenomenal effects produced upon groups of our forest trees may be traced to the mycelium fungus described by the Baron'.
Please cite as “FVM-95-10-25c,” in Correspondence of Ferdinand von Mueller, edited by R.W. Home, Thomas A. Darragh, A.M. Lucas, Sara Maroske, D.M. Sinkora†, J.H. Voigt† and Monika Wells accessed on