SUPRA-MAXIMAL TEMPERATURES 



231 



differently. Humboldt 1 states that the roots of various plants grow in the hot 

 springs of Trinchera (Caracas) at temperatures reaching 85 C, but this requires 

 further proof. Fleshy leaves exposed to sunlight may reach a temperature of 52C., 

 which is fatal to them if unduly prolonged. The fact that plants grow when 

 exposed to full sunlight shows that these temperatures can be withstood for a short 

 time, though not always without injury 2 . Drops of water may also concentrate 

 the sun's rays sufficiently to produce local injury 3 . Dried mosses and lichens 

 are able to maintain themselves on dark exposed rocks which grow very hot during 

 prolonged insolation 4 . 



De Vries exposed plants for fifteen minutes to various temperatures, the roots 

 being in water or soil, the shoots in air, or in water when cuttings were used 5 . 

 Mosses and algae were placed under water. In this way the following table was 

 constructed, in which the columns marked A give the highest temperatures at which 

 the plants were uninjured, and those marked B, the temperatures which caused 

 death. 



1 Cf. Bot. Ztg., 1876, p. 783. 



3 Cf. Ewart, The Effects of Tropical Insolation, Annals of Botany, Vol. xi, 1897, p. 439; 

 Vol. xii, 1898, pp. 384-9. 



3 Frank, Krankheiten d. Pflanzen, 1895, 2. Aufl., Bd. I, p. 175. 



* Kerner and Oliver, Natural History of Plants, Vol. I, p. 554. 



5 De Vries, Mate"riaux p. 1. connaissance d. I'influence d. 1. temperature s. 1. plantes, 1870, 

 p. 3 (repr. from Archives Neerlandaises, T. in). For further details see Meyen, Physiologic, 1838, 

 Bd. II, p. 313; Edwards and Colin, Ann. d. sci. nat., 1834, 2 e se"r., T. I, p. 263; Heinrich, 

 Versuchsstat., 1870, Bd. xni, p. 148 (Hottonid)\ Velten, Flora, 1876, p. 212 (Vallisneria} ; 

 Scheltinga, Bot. Jahresb., 1876, p. 719 (water-plants) ; Schultze, Protoplasma d. Rhizopoden 

 und Pflanzenzellen, 1863, p. 48 ; Strasburger, Wirknng des Lichtes u. der Warme auf Schwarmsporen, 

 1878, p. 61 ; Ewart, On Protoplasmic Streaming, 1903, pp. 59-66 (streaming cells). Kiihne (Unters. 

 uber d. Protoplasma, 1864, p. 87) states that the plasmodia of Aethalium. septicum die after 

 two minutes' warming to 43 C., and those of Didymium serpitla after short heating to 35 C. 



