THE 
HEW PHYTOhOGIST 
Yol. 2, No. 10. December 22ND, 1903. 
ON STIMULUS AND MECHANISM AS FACTORS 
IN ORGANISATION. 
By J. Bretland Farmer, F.R.S. 
(Concluded front Page 201.) 
It cannot be too forcibly insisted on that life, in its manifestations , 
is only recognisable as a series of responses to stimuli. Growth, 
one of the commonest phenomena, is clearly of this order. The 
stimuli are essentially given by the nutrition that is supplied to the 
growing parts, but here again the nature of the structure that will 
appear at any point as the result of a nutritional stimulus able to 
set the synthetic processes at work, will be determined not only by 
the stimulating substance, but also by the nature of the stimulated 
body at the time. Both are effective in producing the final result. 
One can hardly suppose that food-material, for example, flows 
upwards into shoots to settle there as shoot-forming stuff; or that 
root-forming stuff descends to the lower regions, in obedience with 
» 
some geotropic sensitiveness, to make a root-forming mother liquor. 
How would it be possible on this hypothesis, to explain the formation 
of roots on the shaft of a Martagon lily while the postulated shoot- 
substance in this case flowed farther down to the bulbs and axillary 
buds. Or in the case of plants with creeping basal rhizomes, why 
do the roots and shoots, though all produced in the same zonal 
region of the stem, as in Circaea, still maintain their relative mor¬ 
phological positions in the tangle ? 
But although there is strong evidence, from the phenomena of 
growth, that nutritive stimuli do serve as agencies for provoking 
development and increase in the number of parts in the higher 
plants, I believe there is no real evidence that they exceed this role. 
The actual form, the morphological nature, of the organ to be 
produced depends on the stimulated mechanism. Now in speaking 
of a mechanism, I am obliged to use this metaphor because I 
can not think of a better one, but I only mean by it a material 
