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.

Excitatory effects of different rays of light on motile and growing organs are similarly discriminative. Ultra-violet light exerts the most intense reaction which reaches a minimum towards the less refrangible red end of the spectrum. Beyond this, the infra-red or thermal rays become suddenly effective in inducing excitatory movement and retardation of growth.