MOBILE AND IMMOBILE CONDITION, 79 1 



or nine leaves closed; the next morning all the leaves again expanded into their normal 

 diurnal position'. 



TrifoHum incarnatiwi exhibited similar phenomena, with only immaterial differences. 



It is worth noting that in the plants observed by me the positions of the leaves in- 

 duced by the rigidity caused by dark resemble the diurnal more than the nocturnal 

 position of phototonic plants. 



(4) T^ransitoty rigidity from drought I have observed only in Mimosa pudic a. If the 

 earth in the pot in which a plant is growing is left unwatered for a considerable time, 

 the irritability of leaves perceptibly diminishes with the increasing dryness, and an almost 

 complete rigidity ensues, causing the common petiole to assume a horizontal position, 

 and the leaflets to expand. Leaves which have lost their irritability are not withered 

 nor flaccid ; but the watering of the soil causes a return of the irritability within two or 

 three hours. 



(5) 'Transitory rigidity resulting from chemical influences. In this category I include 

 especially the condition termed by Dutrochef" Asphyxia, which occurs in Mimosa when 

 placed in the receiver of an air-pump. While the air is being pumped out, the leaves 

 fold up, no doubt in consequence of the concussion ; but the leaflets then expand, the 

 petiole becomes erect, and while the leaves assume the same position as after pro- 

 longed withdrawal of light, they now remain rigid and possess neither periodic motility 

 nor irritability to concussion. When brought again into the air the plant again becomes 

 motile. It can scarcely be doubted that the eftect of the vacuum is essentially a result 

 of the removal of the atmospheric oxygen, and therefore causes rigidity by suspending 

 the respiration. 



Kabsch^ confirmed these statements, and showed that the stamens of Berberis, Ma- 

 honia, and Helianthemum also lose their irritability in vacuo, regaining it in the air. 



The cessation of the irritability of the stamens of these plants which Kabsch states to 

 take place when they are placed in nitrogen or hydrogen gas may also be ascribed to a 

 simple suspension of respiration, the irritability returning on access of air. The destruc- 

 tion of the irritability which takes place, on the authority of the same observer, in the 

 stamens of Berberis in pure carbon dioxide or in air containing more than 40 p. c. of this 

 gas must, on the contrary, be considered a positively injurious chemical action of the 

 nature of poisoning. If they remain from three to four hours in carbon dioxide, the 

 irritability returns only after some hours on replacing them in air. Carbon protoxide 

 mixed with air in the proportion of from 20 to 25 p. c. destroys irritability, while nitrous 

 oxide produces no effect. The stamens, on the other hand, bend towards the pistil in 

 nitrous oxide, and lose their irritability in i| or 2 minutes. Ammoniacal gas appears 

 to cause transitory rigidity after a few minutes. 



Kabsch states that rigidity ensues after from i| to 2 hours even in pure oxygen, the 

 stamens again recovering in the air. The vapour of chloroform causes transitory rigidity 

 in the leaves of INIimosa, either in the expanded or in the folded position caused by 

 irritation*. 



1 [Bert (Bull, de la Soc. hot. de France, vol. XVII. 1871, p. 107) found that the irritability of the 

 leaves of Mimosa was destroyed by placing them under bell-glasses of green glass almost to the 

 same extent as if placed in the dark; the plants being entirely killed in twelve days under blackened, 

 in sixteen days under green glass ; plants placed in the same manner beneath white, red, yellow, 

 violet, and blue glasses being still perfectly healthy and sensitive, though varying in the rapidity of 

 their growth. — Ed.] 



2 Dutrochet, Mem. pour servir, vol. I, p. 562. 



3 Kabsch, Bot. Zeit. 1862, p. 342. 



* [J. B. Schnetzler (Bull, de la Societe vaudoise des Sciences naturelles, 1869) points out that the 

 substances which destroy the contractility of animal ' sarcode ' also destroy the irritability of the 

 stamens of Berberis and the leaves of Mimosa. Curare has no prejudicial effect in either case ; 

 while nicotine, alcohol, and mineral acids destroy both. In the Comptes rer.dus for April 23rd, 



