322 TEMPERATURE OF PLANTS. 



projects beyond the flower, and is jointed. At the articulation an 

 irritable swelling occurs, which when touched or acted upon by heat 

 and light, causes a sudden incurvation by which the column is thrown 

 to the opposite side of the flower, bursting the anthers and scattering 

 the pollen on the central stigma. After a time the column recovers 

 its position. These movements take place in the flower for some time 

 after it has been removed from the plant and kept in water (^[ 497). 

 Certain petals in some flowers, as in Orchidacese, are said to move. 

 Morren notices this in the case of species of Megaclinium and Pteros- 

 tylis. Gentiana sedifolia closes its petals when touched. Draksea 

 elastica, a Swan River terrestrial Orchid, is remarkable for the irrita- 

 bility of the stalk of the labellum. This stalk exhibits a moveable 

 joint like an elbow. 



666. Chemical agents have an effect on the movements of plants. 

 Some act by causing irritation, others by destroying irritability. Nar- 

 cotic poisons, as opium, belladonna, and hydrocyanic acid, either 

 taken up by the roots or applied externally, destroy the irritability of 

 plants. They cause closure of the leaves of the sensitive plant, and 

 render it insensible to the action of stimuli. Their prolonged action 

 causes death, but if they are applied in moderate quantity, the plant 

 may recover, and again unfold its leaflets. It frequently happens, 

 however, that the irritability continues for some time much impaired ; 

 so that mechanical stimuli do not act in the same rapid and energetic 

 manner as at first. Similar effects are produced by ether and chloro- 

 form when sensitive plants are introduced into an atmosphere through 

 which these substances are diffused. The effects may be produced 

 locally by applying the vapour only to certain parts of the plant. 

 Experiments on the action of poisonous agents, both in the fluid and 

 gaseous state, have been performed by Marcet, Christison, Turner, 

 and others (IT 292296).* 



2. TEMPERATURE OF PLANTS. 



667. The heat developed during the expansion of flowers and the pre- 

 paration of the pollen, especially in the case of Aroideas, and also at the 

 period of germination, has been already considered (^f 475, 476, &c.) 

 These phenomena appear to be strictly of a chemical nature, and may 

 be traced to the absorption of oxygen, and its combination with the 

 carbon of the starch, the latter being converted into dextrine and 

 grape sugar. It is now proposed to consider the observations which 

 have been made relative to the general temperature of plants. 



