6o 
The Queensland Naturalist. 
April, 1928 
These are not shade lovers, but grow in rain forests with 
their tops out in full sunlight. They grow very: rapidly 
and before they can be suppressed by lack of light have 
their tops sufficiently illuminated. Size with these gums 
is not an indication of age. Giants of the Australian 
forests are often not more than fifty years old, and such 
rapid growth is as useful as a long suppression period. 
Most Euealypts, however, are not able to compete with 
rain-forest types. Even those which invade rain forests 
in Queensland, such as E. saligna, usually do so round 
the fringes or along rivers, Where there is more light. 
The fundamental difference between rain forest trees 
and the average Eucalypt has an important bearing on 
the distribution of forests in this State. Rain forest trees, 
being sun lovers which can withstand shade, are capable 
of growing in any place where they have the right tem- 
perature and soil conditions. Euealypts can grow only 
where they have the right temperature, soil, and light 
conditions. Rain forest types may therefore invade the 
open forest and force back the gums, provided there is 
sufficient moisture, but the gums cannot force back the 
rain forest. Now and then we see a gum such as the 
Moreton Bay Ash surrounded by rain forest trees; in 
such cases it is the gum which has been surrounded, not 
the rain forest which has been invaded. 
Blady grass in North Queensland covers great tracts 
of country, it consists of various species of grass several 
feet high, and after bush fires comes up thickly. In 
virgin bush untouched by fire it is not greatly in evidence, 
but burning off provides the sunny condition it needs. In 
the course, of time other plants force their way up through 
it and gradually suppress it. It cannot tolerate shade, 
and ultimately, unless assisted by repeated fires is choked 
out by other sun-loving but taller growing plants. A 
small tree, Miacaranga tanarius, is one of the commonest 
of these, and it in turn may be suppressed by rain forest 
types if there is sufficient moisture in the soil. In the 
Philippine Islands a passion vine, Passillora foetida, 
which is common in North Queensland, is used for sup- 
pressing blady grass (locally known as cogoiB : it makes 
a tangled mass in the shade of which the grass does not 
thrive. 
It is apparent that the light tolerance of plants, 
Therefore, is an important factor in their distribution, 
and also in the re-vegetation or colonization of plantless 
areas. In horticulture, too, it is of considerable import- 
