122 
The Queensland Naturalist August, 1941 
These mycorhizas are of two main types: (a) External 
or ectotrophic , in which the fungal elements are arranged 
in a mantle or sheath over the root as well as between the 
root cells, and (b) endotrophic f in which the fungus is 
internal and appears on the surface of the root as indi- 
vidual hyphae only, with no mantle development. 
The ectotrophic mycorhizas occur in the majority of 
woodland trees and in a few herbs. The endotrophic type 
is the more common and has been found in the majority of 
terrestrial plants in which they have been sought. 
In Eucalyptus and Pinus is found the ectotrophic 
type, whilst in Araucaria and citrus the endotrophic form 
prevails. 
The fact that there is some connexion between tree 
roots and certain fungi was noted as long ago as the third 
century B.C., when Teophrastus commented on the occur- 
rence. But it was not until the nineteenth century with 
the development of microscopic technique that the 
phenomenon became more carefully studied. 
One aspect of interest was the occurrence of the 
truffles beneath forest trees and nowhere else, and it be- 
came general opinion that there must be some symbiotic 
connexion between the two plants — the truffle fungus and 
the beech or other tree. 
The truffle crop is an important one in Europe where 
they are eagerly sought after for marketing purposes. 
Trained pigs are used in hunting for them on account of 
their being able to locate the tubers below the soil surface 
by the scent. Frank, a German botanist, was engaged by 
the German Government in 1880 to investigate truffles so 
as to find some means of increasing the crop. He did not 
succeed in this object but showed that most trees are 
mycorhizal and propounded a theory postulating the 
mutual benefit obtained by the fungus and tree. Most 
botanists of the time, including Hartig, derided Frank's 
ideas, but recognised the presence of fungus structures in 
the roots. 
The fact that all the short roots in many trees were 
sheathed in mycelium led Frank to believe that water and 
nutrients entering the tree were obtained from the fungus. 
Much controversy occurred about this, and there were 
many scientists in favour of each view. 
In 1887 Frank wrote another paper describing the 
