RESPIRATION AND OXYGEN. 93 



(1881) confirmed the results of Wortmann, finding that heliotro- 

 pism and geotropism in Pisum and Triticum were suppressed by 

 nitrogen, hydrogen, and CO2. 



Kraus (1884 : 199) exposed horizontal flower-shoots of Anthriscus, 

 Ranunculus, Taraxacum, etc., to streaming carbon dioxid and hydro- 

 gen. After 6 hours no geotropic effect was visible, but upon expo- 

 sure to the air curvature took place in 5 hours. He regarded this as 

 proof that the plants merely pass into a state of rigor. 



Correns (1892 : 87) made an exhaustive study of the relation of 

 irritability to the presence of oxygen, and at the same time considered 

 the results of Kabsch and Dutrochet. He observed that, at suffi- 

 ciently low pressures, rigidity occurred, the petiole rising and the 

 leaflets closing toward each other. According to Kabsch, reduced 

 pressure effected a movement of the stamens in Berberis and Maho- 

 nia, results verified by Correns. The latter showed also that both 

 hydrogen and nitrous oxid gave similar results, while the sudden 

 increase of the air-pressure did not act as a stimulus. After a period 

 in hydrogen irritability ceased. In pure oxygen the filaments of 

 Berberis did not react, but they remained irritable after 24 hours' 

 immersion. Both Kabsch and Correns found that the filaments did 

 not react to CO2, 50 per cent CO2 destroying irritabihty in 10 minutes. 

 The stigmatic lobes of Mimulus closed under reduced pressure, as 

 they did also in hydrogen. In pure oxygen the stigmas retained 

 their irritability as long as 48 hours. The leaves of Securigera, 

 Tetragonolobus, Oxalis, Lupinus, Trigonella, Medicago, Trifolium, 

 and Amicia lost their irritability under reduced pressure, both night 

 closing and morning opening being suppressed. Oxalis was unable 

 to withstand the lowered pressure and was completely dead after 

 12 hours. For the appearance of sleep movements in Oxalis, 3.5 

 per cent of the oxygen originally present was necessary; for Securi- 

 gera, 5 per cent closed the leaves quickly, while it acted more slowly 

 for Tetragonolobus, Sleep movements ceased in pure hydrogen, as 

 they did in CO2, nitrogen, and nitrous oxid. Correns confirmed the 

 discovery of Wortmann that geotropic movements were suspended 

 in vacua, and that of Wiesner, which gave similar results for heHo- 

 tropic movements. He also corroborated the results of Wieler as to 

 the cessation of growth in the absence of oxygen. He noted that 

 the growth of shoots ceased before that of seedlings, and that shoots 

 of Helianthus died at 1 per cent of the original amount of oxygen, 

 and Vicia at 2 per cent. 



Reduction of the pressure did not produce reaction in tendrils, 

 though they responded shghtly to contact in oxygen-free air. For 

 distinct response the lowest limit was 3 to 4 per cent for Passiflora, 

 Sicyos, and Bryonia, and 2 to 3 per cent for Cyclanthera. In a mix- 

 ture of 12 per cent air and 80 per cent CO 2, irritability was lost in 

 a short time. Reduced pressure did not produce reaction in the 



