772 
Schwartz . — Observations on 
mycorhiza. These swellings are illustrated in Figs. 7 and 8. In the former 
figure the swelling is giving rise to a tube which is penetrating a neighbouring 
mycorhizal cell containing undigested fungal matter. 
For the purpose of comparison, the roots of plants of Asarum euro- 
paeum obtained from the Chelsea Physic Gardens and from the garden of 
Mr. E. M. Holmes, at Sevenoaks, were examined. But in both cases these 
were free from mycorhiza, as were also the roots of Aristolochia Sipho 
obtained from the same sources. It is, however, by no means unusual for 
a mycorhizal fungus to be absent at times from a root, the general rule being 
that when the plant is growing in a soil rich in humus the fungus will be 
present, and that when the soil is poor in humus it will be absent. It may 
be added that the roots of plants possessing the mycorhiza were found to 
possess comparatively few root-hairs, whereas in those which lacked the 
mycorhiza the root-hairs were more abundant. 
Endotrophic and ectotrophic mycorhizas have long been known ; the 
former are commonly to be found in the roots of the Orchidaceae, Ericaceae, 
and Epacridaceae, although the hyphae are never so deeply seated as in 
Asarum europaeum . The ectotrophic forms are to be found in the Cupuli- 
ferae and many of the Gymnosperms, not to mention numerous other orders 
in plants of which they have been observed. 
The mycorhiza of Neottia Nidus-avis , which bears points of similarity 
to that of Asarum, has been investigated by Magnus, in 1900 ( 3 ), who states 
that the fungus enters the root or rhizome, where it branches and fills up 
a series of concentric layers of cells. In some cells it kills the host proto- 
plasm, while in others it is itself killed and partly digested by the plant, the 
indigestible residue aggregating into a ball in the centre of the cell and 
being covered by a membrane. 
In 1904 Ternetz (6) isolated a fungus, which was presumably its 
mycorhiza, from the roots of some of the Ericaceae and stated that it was 
an active agent of nitrogen-fixation from the atmosphere. 
In 1909 Osborn (8) described a fossil mycorhiza found in the lateral 
roots of A my elon radicans . According to this authority, the hyphae are 
non-septate, and they are found in the inner cortical layers of the root, and 
are apparently very similar to those found in Asarum. He states that 
some of the cortical cells are filled with coils of fungal hyphae, whereas 
others, which he designates 1 digestive cells ’, contain irregular masses of 
fungoid matter. The fungus, like that of Asarum, is limited to the inner 
cortical layers of branch roots, and is absent from the tissue of the main 
roots. On some of the hyphae thickened terminal dilatations were found, 
evidently representing a resting stage of the fungus. These dilatations 
correspond with the thick-walled swellings observed by me on some of the 
hyphae in Asarum, and lend support to the view that these swellings belong 
to the mycorhizal and not to some other parasitic fungus. 
