i66 WALTER TRANQUILLINI 



The water loss of leaves of the alpine rose {Rhododendron ferrugineum) 

 clearly exceeds the critical limit at some measurements (Fig. 8). If we cut 

 off twigs of this plant m winter and expose them to the open air in February 

 and March they wilt after only 21 days (Table 3). Twigs of pine trees can 

 endure the same conditions for 49 days. Therefore the alpine rose depends 

 on the protection of a snow cover and grows only in such places which are 

 covered with snow reliably and for a long period during the winter. 



Among the tested plant species the trailing azalea [Loisekuria procumhens) 

 has an exceptional position. When a twig is cut off and is exposed to the air 

 it starts wilting after nearly the same time as a twig of the alpine rose. This 

 is due to the high cuticular transpiration and little water storage in the 

 shoots (Table 3) but in its natural habitat it is not more stressed than are 

 young pine trees (Fig. 8, Table 3). For this phenomenon the only explana- 

 tion is that the azalea is well supphed with water in late winter, although it 

 grows in snowless places (Fig. 5), where the soil is certainly frozen. On warm 

 sunny days during this period there is a lot of water from melting snow, 

 which cannot penetrate into the soil. Therefore it saturates the Utter and 

 mould layer. In this wet layer numerous adventitious roots are spread by 

 which the plant can absorb this water. 



REFERENCES 



AuiiTZKY, H. (1958) Waldbaulich-okologische Frageii an der Waldgrcnze. Cbl. ges. 



Forstwesen, 75, 18-33. 

 AtniTZKY, H. (1961) Die Bodentemperaturverhaltnisse an einer zentral-alpinen 



Hanglage beiderseits der Waldgrenze. Arch. Met. Gcophys. Bioklim. loB, 445- 



532. 

 Berger-Landefeldt, U. (1936) Der Wasserhaushalt der Alpenpflanzen. Bihl hot. 115. 

 Cartellieri, E. (1941) Ober Transpiration und Kohlensaureassimilation an einem 



hochalpinen Standort. Sitzungsher. Akad. Wiss. V/ien, math.- naturw. Kl. Abt. I. 



149, 95-143- 

 DoRiNG, B. (1935) Die Temperaturabhangigkeit der Wasseraufnahme und ihre 



okologische Bedeutung. Z. Bot. 28, 305-383- 

 Hofler, K., Migsch, H. & Rottenburg, W. (1941) Uber die Austrocknungsresistenz 



landwirtschaftlicher Kulturpflanzen. Forschuiigsdiaist, 12, 50. 

 Larcher, W. (1957) Frosttrocknis an der Waldgrenze und in der alpinen Zwerg- 



strauchheide auf dem Patscherkofel bei Innsbruck. Veroff. Ferdinandeum Innsbruck, 



37, 49-81. 



Larcher, W. (i960) Transpiration and photosynthesis of detached leaves and shoots 

 of Quercus pubescens and Quercur ilex during desiccation under standard condi- 

 tions. Bull. Res. Counc. of Israel, 8D, 213-224. 



Livingston, B.E. (1906) The relation of desert plants to soil moisture and to evapora- 

 tion. Carnegie Inst. Publ. 50. 



