200 SECTIONAL ADDRESSES. 
Micrococcus; similar observations have been made on other micro- 
organisms by bacteriologists, and some refer to the condition as one of 
symbiosis. Bacteriologists, I would note, are continuously misapplying 
the term symbiosis in referring to bacteria grown in mixed cultures, 
when there is no evidence whatever that the micro-organisms are 
mutually interdependent for their growth. In passing, it may be men- 
tioned that nodules on the roots of the alder are attributed to the presence 
therein of Streptothrices, and that comparable nodules occur in 
Eleagnacee. The nodules on the leaves of Rubiacee and tropical 
Myrsinacez are also regarded as due to bacterial symbionts. 
(3) The significance of Mycorhiza in relation to various Plants. 
It has long been known that the roots of most perennial and 
arborescent plants are invaded by the mycelium of fungi known as 
Mycorhiza, and it is to Kamiensky (1881), and especially Frank (1885), 
to whom we owe the hypothesis that we are here dealing with symbiotic 
life. Frank distinguishes two forms of Mycorhiza: (1) the ectotrophic, 
which surround the root externally like a sleeve and are found especially 
about the roots of forest trees (Conifers), and (2) endotrophic, which 
penetrate deeply into the root tissue and even into the cells of the root. 
The endotrophic Mycorhiza are derived from the outside ; their mycelium 
enters the root by penetrating the epidermal cells at the base of the 
root hairs, passes between the cells and into them where the mycelium 
branches dichotomously, and forms ultimately a much-branched intra- 
cellular growth. By this time the fungus is no longer in communica- 
tion with the exterior of the root, and it nourishes itself within the 
host cell, only, however, by utilising the reserve substances stored there 
whilst avoiding the cell protoplasm or other living host elements. The 
host cell, after a period of inertia, exhibits a distinct reaction to the 
presence of the fungus, in that its nucleus becomes hypertrophied, 
divides repeatedly and becomes amcebiform in contour. The contained 
mycelial mass undergoes degeneration, is digested by the host, and the 
host-cell resumes its normal life. These root-Mycorhiza have not as 
yet been cultivated,’ as have others to which reference will presently be 
made, and it is as yet impossible to assign them a place among known 
species of fungi. Further details regarding these forms will be found 
in the publication of Gallaud (1904). 
Mycorhiza in Orchids. 
The first to note the presence and to attempt to cultivate the fungus 
mycelium in the roots of orchids was Reisseck (1846), and in 1881 
Kamienski advanced the hypothesis that the association was one of 
symbiosis. Wahrlich (1889) subsequently found symbionts in all 
species of orchids he examined, about 500 in number, thereby showing 
that their distribution is generalised. 
It is to the researches of Noél Bernard (1902 onward), however, that 
we are actually indebted for the complete demonstration of the true 
* Magrou (1921) reports that he isolated Mucor solanum n. sp. from Solanum 
dutca-mara, and he seems to have infected the potato plant with the fungus. 
oe + in 
