Honoured Sir,— In reply to your letter concerning the question whether the water weeds
, which covers the lagoon at your town, should be removed,
I am of opinion that it would be advisable to do so, particularly before it commences
to decay largely, when the weather becomes hot, and the water gets shallow, as then
the purifying influence of new growth may be out of proportion to the mass of decaying
particles; moreover in the numerous capillary Azolla rootlets, many kinds of minute acquatic organisms would be harboured, the accumulating
quantity of which act deteriorating on the water by casting off as a whole copiously
and constantly lifeless particles. If, constantly, a vigorous growth of such a plant
as the Azolla occured in water, of some depth, the existence of this plant anywhere in huge quantity,
may not be harmful, or by its decomposing action and by its respiration even beneficial
to the water: but in hot summer weather, soon approaching, and when the water will
become heated, also, and, by evaporation, much reduced, it seems to me advisable to
guard as much as possible against the accumulation of any organic matter, which may
give rise to malarian exhalations, and may render such water unwholesome for drinking
purposes. Thus the wafting of foliage from trees into such lagoons should also be
prevented, although the leaves of
and of the most terebinthine pines do not cause any danger in this respect on account
of the antiseptic oil pervading them. To prevent the possible inflow of sewage and
impure surface water into rivers, ponds or swamps, should such danger anywhere exist,
I have on former occasions elsewhere advised to plant at some distance from the shore,
or from the margin of the water, belts of our most anti-miasmatic eucalypts and of
bamboos or bamboo reeds, as the roots of these would much intercept and largely absorb
the impurities of the inflowing humidity, the creation of such eucalyptus and bamboo
belts not being costly, and adding beauty to the landscape also. I have the honour,
Mr Mayor, to be your obedient
Ferd. Von Mueller.
