PLANT PHYSIOLOGY 55 



was maintained constant, the subsequent presentation time in 

 weaker light increased with increase in intensity of the 

 original light. Three stages could be observed in the re- 

 sponse : a slowing down of the original movement, a rest 

 period, and recommencement of movement, but in the opposite 

 direction. 



Movements which at first sight appear to be regulated by 

 light, but which in reality are dependent upon temperature, 

 have been investigated by Lundegardh (" tjber Bliitenbewegun- 

 gen und Tropismen bei Anemone nemorosa," Jahrb.f. wiss. Bot., 

 57, 80-94, 1917)- The mature flowers of Anemone nemorosa are 

 fully opened and turned towards the sun at midday, while at 

 night, or in rainy weather, they are closed and bent downwards. 

 Lundegardh finds these movements are not dependent on light 

 but are thermonastic. The flower stem is, nevertheless, 

 strongly phototropic. The thermonastic movements occur 

 both in the flower and the flower stalk, the flowers opening when 

 the flower stalk is just erect, and closing when the stalk begins 

 to curve. These nastic movements are stopped by anything 

 which brings about a cessation of growth, whence it is con- 

 cluded that they arise by growth differences, and not by 

 different turgor conditions in the cells on different sides of the 

 organs. 



A long investigation on thermotropism has been made by 

 R. Collander (Dissertation, Helsingfors, 95 pp., 1919). Shoots 

 of seedlings of Avena, Helianthus, Lepidium, Vicia, and Zea all 

 exhibited positively thermotropic curvature, probably due to 

 slower growth on the concave than on the convex side. These 

 curvatures were only observed at temperatures above the 

 optimum for growth. Radicles exhibited a positively ther- 

 motropic curvature at lower temperatures and a negatively 

 thermotropic curvature at higher temperatures. Even the 

 positive curvature is preceded by a negative one. No thermo- 

 tropic curvature was observed in Phycomyces. 



In this last-named fungus Elfving had shown as long ago 

 as 1890 that a number of substances could bring about a 

 chemotropic curvature of the sporangiophore. The same 

 worker has now shown that this curvature is in reality an 

 aerotropic one, that is, one due to a change in composition of 

 the atmosphere. (" Phycomyces und die sogenannte physiolo- 

 gische Fernwirkung," Ofvers. Finsk Vet. Soc. Fork., 59, Afd. A, 

 No. 18, 56 pp., 1917). The " metallotropic " curvatures 

 induced by iron and other metals are produced partly by 

 absorption of gases from the surrounding air, partly by oxidation 

 of the metals which is probably accompanied by the formation 

 of ozone. Many odoriferous substances are capable of inducing 

 similar curvatures. 



