fungi, all contribute their quota of food for epiphytes. Although Orchids gener- 
ally are considered to be non-parasitical, I am inclined to think that certain 
species may obtain at least part of their nutrition from the bark or sap of their 
host. This appears to be the case with those species which invariably are found 
growing on a particular species of tree. Dendrobium Toff tii, one of our finest nat- 
ive species, almost invariably is found growing upon certain species of man- 
grove, although other trees quite generally suited to them, are growing in con- 
tiguity. This may, of course, be quite coincidental, but I am inclined to think 
that probably D. Tofftii gets some of its nutriment either from the sap of the man- 
grove, or from some element of its bark, or possibly from some particular fungus 
growing upon it. 
The great bulk of the genera and species of Orchids cultivated by us orig- 
inate in the tropical band encircling the earth and covering the area of its surface 
between latitudes 20 degrees north and 20 degrees south. In this band, nearly 
3,000 miles wide, the climate naturally varies somewhat, due to different factors 
such as elevation, surface conformation, contiguity to the ocean, and so on, but 
in most of the areas where our Orchids grow, the climates come under Koppens 
classifications, Af., Am., and Aw. These are all much alike, the main difference 
being in the amount of average rainfall during the dry period of the year. The 
essential features of these climates are that they have a heavy rainfall for at least 
nine months of the year, so that even in the winter, or during a dry period, the 
ground is damp, causing constant atmospheric moisture by evaporation; wacm 
conditions, which vary little between winter and summer; and strong sunlight for 
the greater part of the year. We naturally try to give the plants in our care 
something of the same conditions. ‘This means that for the greater part of the 
year we are applying considerable quantities of water to our plants, so that all 
through the warm period the compost in which they grow is kept uniformly 
moist. 
Now, Orchids absorb the necessary elements of their nutriment 
from the water of their compost. This water, by the process of 
osmosis, has attracted the molecules of nitrogen, potassium, and _ other 
chemicals from the humic compost; and the plant selects from the water 
such of these elements as it requires at the moment. When first potted in suit- 
able compost there are ample supplies of food available. Naturally only a little 
of the water is absorbed at a time. This means that right throughout the warmer 
period of the year (nearly 9 months in Brisbane) a tremendous quantity of water 
is passing through the compost and collecting, in its passage, minute particles of 
plant food. Most of this water is lost by drainage or by evaporation, so that 
quite a large proportion of the plant food is simply carried away unused, There- 
fore, after some months the compost has had its stores of food elements consider- 
ably depleted, and this depletion continues to increase in ratio to the disinte- 
gration of the compost material. 
If we could repot our Orchids every few months, or even every year, and 
give them a new compost to work upon, this wastage of food would not matter. 
Of course this is physically impossible for most of us—we haven’t the time to 
set ean 
