| Specimen. | Effect of rise of temperature. | Effect of stimulus. |
| Zephyranthes (positive type). | Movement of opening | Movement of closure. |
| Nymphæa (negative type). | Movement of closure | Movement of opening. |
In Nymphæa it is the outer side of the perianth that is relatively the more excitable since diffuse electric stimulus induces a movement of opening due to the greater contraction of the outer side. It is by the greater expansion of this more excitable side that the movement of closure is effected during rise of temperature.
From the results of experiments given above we arrive at the following:—
LAW OF THERMONASTIC REACTION
RISE OF TEMPERATURE INDUCES A GREATER EXPANSION
OF THE MORE EXCITABLE HALF OF AN ANISOTROPIC ORGAN.
SUMMARY.
Thermonastic movements are induced by the differential physiological effect of variation of temperature on the two halves of an anisotropic organ.
Rise of temperature induces greater expansion, and enhancement of rate of growth of the more excitable half of the organ; lowering of temperature induces the opposite effect.
Two types of thermonastic movements are met with, the positive exhibiting a movement of opening during rise of temperature; in these the inner half of the organ is relatively the more excitable. Example of this is seen in the Crocus and in Zephyranthes.
In the negative type, rise of temperature induces a movement of closure. Here the outer half of the organ is the more excitable. The flower of Nymphæa belongs to this type.
The effect of stimulus is antagonistic to that of rise of temperature. In positive thermonastic organs stimulus induces a movement of closure; in the negative type it induces a movement of opening.