46 THE FACTORS [Part I 



which are chiefly concerned with the oecological optimum. As an example, 

 the following tabular statement prepared by Detmer 1 is here reproduced : 



This table shows very clearly that the cardinal points of germination are 

 higher for plants from warm countries than for those from cold ones. But 

 these figures are too high in some cases, and by no means properly repre- 

 sent the great inequality of temperatures which are effective during germina- 

 tion in different climates, for, on the one hand, they do not deal with any 

 purely tropical plants, and, on the other hand, some of the minima for 

 temperate plants are too high. The degrees of temperature given for the 

 minima by F. Haberlandt are more instructive. Sinapis alba, Camelina 

 dentata, Trifolium hybridum, and Medicago sativa not only germinated 

 between o° and i° C, but also made considerable further progress in 

 development. Of plants from hot countries, Solatium Melongena, Nicotiana 

 Tabacum, and Cucurbita Pepo germinated between ii° and 16 C, but 

 Cucumis sativa, C. Melo, and Theobroma Cacao only above 16 C. Uloth 

 observed the germination of several grasses, Cruciferae and Papilionaceae, 

 at o° C, but the process was very protracted. Kerner placed glass tubes 

 containing earth and seeds in a spring, the temperature of which remained 

 constant at 2 C, and he found that numerous alpine plants germinated 

 even at this low temperature. 



Growth depends on conditions of temperature similar to those required 

 for germination, which partially consists of processes of growth. There 

 are plants on alpine heights, but especially in the polar regions, that can 

 grow considerably at a temperature approaching the freezing-point. Thus 

 the flowers of Soldanella alpina break through the snow, and those of 

 Anemone vernalis, Crocus vernus, and other species appeared to me to 

 be quite as accommodating, as I found them in half-melted snow ; but 

 owing to direct insolation, even through thin layers of snow, a higher 

 temperature than o° C. may be reached in such cases. Even more remark - 



1 Lehrb. d. Pflanzenphysiol., p. 269. 



