Orchid Mycorrhiza. J. Ramsbottom. 55 
sponding to the presence of mycelial filaments suggests that the 
latter take up the functions of the former. Later, the view taken 
was that the fungus does not necessarily nourish the roots, but 
draws its nutriment from the humus of the soil and passes on 
a portion of this to the roots. In other words the presence of 
the fungus allows the root to make use of certain substances of 
the humus that it would be incapable of utilizing in its absence. 
Another hypothesis which figures largely in the literature of the 
subject is that of Stahl*. This author endeavours to show that 
the réle of the fungus consists in furnishing the plant with 
mineral nutriment. Comparing plants with and without mycor- 
rhizas he points out certain differences which always appear to 
indicate a much greater circulation of water in the latter. Thus 
their roots are strongly developed, they possess numerous root 
hairs, their leaves transpire energetically and are often provided 
with water stomata. Further, their tissues are ordinarily rich 
in starchy matters and poor in sugar, i.e. in a condition favour- 
able for transpiration. The fact that mycotrophic plants tran- 
spire lesst and are in consequence less well fed in nutrient soils 
leads to the idea that the service which the fungus renders to 
the host consists in remedying the insufficiency of transpiration. 
Stahl imagines that the fungus hands over the products of 
assimilation of the salts rather than the salts themselves. There 
exists between phanerogams and fungi growing in the humus of 
forests, heaths, moors, etc., a competition for the salts which 
the vegetable débris already contains in a concentrated form. 
The advantage in this struggle would apparently be on the side 
of the fungi owing to their mode of life. Plants with very active 
transpiration are alone capable of struggling with success against 
fungi in soils rich in humus: plants with feeble transpiration 
are only able to subsist in these conditions by the help which 
their symbiotic fungus brings. 
Magnus (1900) from his anatomical investigations regarded 
the digesting cells as serving for absorbing the nutriment of the 
fungus: the lodging cells, on the other hand, are set apart for 
the nourishment of the fungus on the cell contents and for its 
hibernation. This idea would give the classical balance of 
symbiosis—each component benefiting to an approximately 
equal degree. 
Gallaud regards the communication of thé endophyte with 
the exterior in endophytic mycorrhizas as insufficient to assure 
to the plant the absorption of nutritive substances. From a 
* E. Stahl, Der Sinn der Mycorrhizenbildung. Jahr. f. wissensch. Bot. 
XXXIV, Pp. 539-668 (1900). 
¢ The difficulty in drying orchid plants for herbarium purposes is a result 
of this. 
