There is no breach of continuity in the increasing contractile reaction in a growing organ under increasing intensity of stimulus; the incipient contraction seen in retardation of rate of growth culminates in a marked shortening of the length of the organ.
Time relations of response, the latent period, the apex time, and the period of recovery are of similar order in pulvinated and in growing organs.
In condition of sub-tonicity the pulvinus of _Mimosa_ responds to stimulus by an abnormal _positive_ or erectile response. Under continued stimulation the abnormal positive is converted into normal _negative_. Growing organs in sub-tonic condition responds to stimulus by abnormal acceleration of rate of growth, which is converted into normal retardation under continuous stimulation.
Direct stimulus induces in _Mimosa_ a _negative_ response, with the fall of leaf. But Indirect stimulus induces the _positive_ or erectile response. Similarly, Direct stimulus induces in a growing organ a _negative_ variation, or retardation of rate of growth, and Indirect stimulus a _positive_ variation or acceleration of rate of growth.
The electric response to Direct stimulus is by galvanometric _negativity_, that to Indirect stimulus by galvanometric _positivity_.
Under condition of sub-tonicity the autonomous activity of leaflet of _Desmodium gyrans_ and of growing organs comes to a stop. The arrested activity in both is revived by the application of stimulus. Active pulsation in _Desmodium_, and active growth in growing organs are, however, retarded or arrested by stimulus.
The contractile effect of stimulus on pulsation of leaflets of _Desmodium gyrans_ is seen by the reduction of the diastolic limit of its pulsations; to this corresponds the incipient contraction and retardation of rate of growth in a growing organ. The effect of warmth is antagonistic to that of stimulus. The expansive effect of rise of temperature is seen in _Desmodium_ by the reduction of the systolic limit of its pulsation; in growth it is exhibited by an acceleration of the rate of growth.
All stimuli which induce an excitatory contraction and fall of the leaf of _Mimosa_ also induce incipient contraction and retardation of rate of growth in a growing organ.