422 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1914. 
no shuddering twitch, either mechanical or electrical; and that even 
in the sensitive Mimosa, an irritation does not cause an excitatory 
impulse, but a mere hydraulic disturbance. The pendulum then 
swings from these hasty assumptions to the diametrically opposite 
extreme. Under these circumstances the clear path is that which 
leads us away from theory and disputations to find the thread of fact. 
We must, therefore, abandon all our preconceptions, and put our 
questions direct, insisting that the only evidence which can be 
accepted is that which bears the plant’s own signature. 
How are we to know what unseen changes take place within the 
plant? If it be excited or depressed under some special circum- 
stance, how are we, on the outside, to be made aware of it? The 
only conceivable way would be, if that were possible, to detect and 
measure the actual response of the organism to a definite testing 
blow. When an animal receives an external shock, it may answer 
in various ways; if it has voice, by a cry; if it is dumb, by the 
movement of its limbs. The external shock is the stimulus; the 
answer of the organism is the response. If we can find out in the 
plant the relation between the stimulus and response we shall be 
able to determine its state of vitality at the moment. In an excit- 
able condition, the feeblest stimulus will evoke an extraordinarily 
large response; in a depressed state even a strong stimulus evokes 
only a feeble response; and lastly, when death has overcome life, 
there is an abrupt end of the power to answer at all. 
We might, therefore, have detected the internal condition of the 
plant, if we could have made it write down its responses. In order 
to succeed in this, we have, first, to discover some compulsive force 
which will make the plant give an answering signal; secondly, we 
have to supply the wherewithal for an automatic conversion of these 
signals into an intelligent script; and, last of all, we have ourselves 
to learn the nature of the hieroglyphic. 
RESPONSE OF PLANT AND ANIMAL. 
In answering the question whether there is a fundamental unity 
in the response of plant and animal, we have first to find out whether 
sensitiveness is characteristic of only a few plants or whether all 
plants and every organ of every plant is sensitive. Then we have to 
devise apparatus by which visible or invisible reactions are detected 
and recorded. Having succeeded in this, we have next to survey 
the characteristic reactions in the animal, and find out whether 
phenomena corresponding to these may also be discovered in the 
plant. 
Thus, when an animal is struck by a blow, it does not respond at 
once. <A certain short interval elapses between the incidence of the 
blow and the beginning of the reply. This lost time is known as 
