_c._ Anisotropic thick organ; transverse conduction possible. Thick line represents the more excitable distal side. Sequence of curvature: positive, neutral and pronounced negative. When light strikes from opposite direction on the more excitable side the curvature will remain positive, since the pronounced reaction of the more excitable side cannot be neutralised or reversed by transmitted excitation to the less excitable distal side (_e.g._, leaf of _Mimosa_). _In the absence of transverse conduction_, the curvature remains positive (_e.g._, leaflet of _Erythrina_). _d._ Anisotropic thin organ with high transverse conductivity. Sequence of curvature: transient positive, quickly masked by predominant negative. Light striking on the more excitable side will give rise only to _positive_. The response in relation to the plant, will apparently be in the same direction whether light strikes the organ on one side or the opposite (_e.g._, leaflets of _Mimosa_, _Averrhoa_ and _Biophytum_). I have shown that tissues in sub-tonic condition exhibit an acceleration of the rate of growth under stimulus (p. 224) the corresponding tropic reaction would therefore be away from stimulus or _negative_ curvature. The tonic condition is, however, raised to the normal by the action of stimulus itself, and the tropic curvature becomes positive. I give below a table which will show at a glance all possible variations of phototropic reaction. TABLE XXXI.--MECHANICAL RESPONSE OF PULVINATED AND GROWING ORGANS UNDER LIGHT.