182 TRANSACTIONS AND PROCEEDINGS OF THK [Sess. lxvi. 



of pushing will cause to pass the dead point — the dead 

 point here being the horizontal for diffuse light and the 

 vertical for sunlight. 



Under this category also come cases of attunement of 

 Algie to light of particular intensity (Detmer, " Physiology," 

 p. 426). 



Temperature. — Temperature variations induce growth 

 variations in the course of a few hoifrs. This period of 

 anabolic inertia is relatively short when contrasted with 

 that following variations in the other tonic conditions, 

 such as pressure of oxygen or food supply (Pfeffer, 

 "Physiology," pp. 511, 512). A rise of temperature from 

 15°— 20°C. stimulates tulip and crocus ilowers to open 

 after a latent period — anabolic phase— of five minutes or 

 so. If while opening the temperature be reduced, they 

 close, but not immediately ; in virtue of their katabolic 

 inertia they continue to open for a few minutes. Pfeffer 

 states that the tulip is sensitive to a differeilce in 

 temperature of ^° C, while the crocus to 2° or 3°C. The 

 former thus has much less functional inertia to change of 

 temperature than the latter. 



At 40° C, protoplasmic streaming is inhibited in Elodca 

 after the short period of two minutes — katabolic inertia — 

 while recovery requires 1—2 hours, a relatively prolonged 

 period of anabolic inertia (Detmer, "Physiology," p. 420). 



In response to the directive stimulus of the heat rays, 

 Lcpidium seedlings execute negative thermotropic curva- 

 tures, while Zea seedlings exhibit positive thermotropism. 

 In both cases the curvature begins only after the lapse of 

 a few hours — anabolic inertia. 



Coiitad.— Taking cases of contact irritability as exempli- 

 fied in tendril climbers, insectivorous, and sensitive plants, 

 we find that they display functional inertia under varied 

 aspects, e.g. phenomena of latent and refractory periods, 

 physiological insusceptibility, and specific idiosyncracy. In 

 the different species of Droscra the latent period varies 

 from ten seconds to twenty minutes (Darwin, " Insecti- 

 vorous Plants "), while in the tendrils of the Passijlorece 

 it may be from a few seconds to an hour (MacDougal, 

 "Annals of Botany," vol. x. p. 373). In contrast to the 

 above, Dioiicea and Mimosa have relatively so little ana- 



