234 PROCEEDINGS OF SECTION D. 
as long as broad. But Mr. Fitzgerald’s figure of the plant shows 
the leaves nearly as long as broad. The habitat is the same— 
Eucalypts, especially ironbark, and the pine. Mr. Fitzgerald 
remarks that this is one of the few epiphytal orchids which 
habitually grow on Eucalypts. It is the only one so far as I 
know, for Cymbidium always grows, not on the trunk, but in 
spouts, deriving its nourishment from the rotting wood. He also 
says it is impatient of removal to the bush-house or green-house, 
but flowers freely till it dies. This is contrary to my experience, 
as in addition to the one mentioned which I have had eight years 
on my verandah, other plants have lived and flourished with me 
for years. 
The main difference between the northern and southern form 
no doubt arises from environment. Probably the greater heat 
and moisture of the northern river scrubs is the cause. But 
why the difference should be merely one of length of pseudo-bulb 
I confess I do not see. One might reasonably have expected the 
variation to be in the direction of more robust plants, for plant 
food must be more abundantly and regularly supplied in the 
northern localities. Mr. Fitzgerald (loc. cit.) says the flowers are 
finer in the north, but I have not found it so. Some flowering 
plants from Queensland certainly had no more and no finer 
blooms than the average southern plant. 
Dendrobium tetragonum is not a very common orchid in Iila- 
warra. It usually grows on myrtle trees (Backhousia myrti- 
folia), but I have seen it on Lugenia Smith, and on rocks. It 
grows on the same and other trees on the Bellingen River. The 
pseudo-bulbs are four-angled and thin at the base, thickening up 
rather suddenly beyond the middle and thinning again near the 
leaf-bearing apex, the leaves being four or less. The flowers 
spring out from the centre of the leaf cluster, and sometimes 
from the joints of the thick portion of the pseudo-bulb. This is 
the southern form (Fig. 5). But on the Bellingen and Nambucca 
Rivers, and, I have no doubt, on the rivers further north, al- 
though the form and size of the plant is just the same, there is 
still a great difference. From the centre of the leaf cluster, and 
from the joints of the thick portion of the pseudo-bulb, young 
shoots develop into perfect pseudo-bulbs (Fig. 5), and aerial roots 
grow out from their bases and twist over the parent stems, ad- 
hering to them tightly just as the older or primary roots do to 
the tree or other support. The aerial roots develop from the 
joints prior to the appearance of the shoots. 
There can be little doubt but that this proliferation is directly 
caused by the greater amount of moisture present in the atmos- 
phere in the northern localities. Just in the same way adven- 
titious roots are more common in the fig-trees on the north coast 
than in Illawarra (where, indeed, they seldom occur, and then 
only in favourable surroundings, as when they overhang creeks, 
