NOTES. 
ON THE CAUSE OP PHYSIOLOGICAL ACTION AT A 
DISTANCE l . — Most vegetable organs are sensitive to the influences 
of the environment and respond to these stimuli, as long as they are 
capable of growth, by bending in a definite direction. In fact, they 
generally feel asymmetrical distribution of matter or energy around 
them. Thus, the geotropic, heliotropic, hydrotropic, haptotropic 
curvatures arise, which are familiar to vegetable physiologists. 
But the very interesting phenomena described two years ago 
by Elfving did not appear to belong to any of the known categories, 
and led this distinguished botanist to the assumption of a new force 
revealing itself by ‘ physiological action at a distance ' — as he 
terms it. 
He found that pieces of iron and, to a less degree, of zinc or 
aluminium, as well as different organic substances, such as sealing- 
wax, rosin, roots of living plants, attract the growing sporangium- 
bearing filaments of Phycomyces nitens , a well-known fungus 
belonging to the Mucorini. All other metals tried by Elfving 
were inactive, whereas the filaments of Phycomyces itself showed 
a mutual repulsion. 
The latter fact, which I had often observed, I always ascribed 
to negative hydrotropism. So the question arose whether the 
attractions discovered by Elfving are not due to a similar cause. 
For, just as we know that a surface which emits moisture repels 
the Phycomyces filaments, it seemed probable that moisture-absorbing 
substances should produce the reverse effect and attract them. Now 
iron certainly absorbs aqueous vapour whilst rusting, and its peculiar 
action on Phycomyces might thus be simply a case of hydrotropism. 
I have tested this view by a great number of experiments, and 
I submit for the inspection of the members of this section photo- 
graphs showing the behaviour of Phycomyces towards different 
1 Read before Section D of the Brit. Assoc, on the 5th of August, 1892. 
