544 FREEZING AND BURNING. 



their functions as in the previous summer, the flower-buds opened, and new inflor- 

 escences sprang from the axils of the leaves, proving that the protoplasm of this 

 plant had not been killed even by a temperature of —46°. 



Myrtle and orange trees freeze dead from —2" to —4°, cypresses and fig-trees 

 from —7° to —9°; vines at —21, oaks and beeches at —25', plums and chemes 

 at —31°, and apple and pear trees at —33°, and this can only be explained by the 

 specific constitution of the protoplasm. We are forced to assume that the cell-body 

 is destroyed in one case by a certain temperature, and in another by a different 

 temperature, in the manner already described. 



It has been previously remarked that the temperature at which freezing takes 

 place also depends upon the stage of development of the plants. It is general!}^ 

 known that woody trunks and branches, foliage, and flower-buds, and especially 

 seeds Vjear quite extraordinary winter temperatures when they have been poor in 

 water in the autumn. In Yakutsk and Werchojansk in Siberia, where the mean 

 temperature in January amounts to — 42'8° and — 49'0°, and where — 62'0'" and 

 — 63"2 (the lowest temperature hitherto generally observed on the earth) were 

 noticed, where for months the temperature in the shade does not rise above —30°, 

 numerous herbs and shrubs are found whose upper organs ai-e exposed for weeks 

 to a degree of cold at which mercury freezes; even birches and larches flourish 

 there with the most vigorous growth, and there can be no doubt that the wood and 

 buds of these trees are every year cooled down for a long time to —30°, and yet 

 are not frozen. Moreover, eveiy winter the wood of the juniper and of spruce, of 

 silver firs and arollas sinks down to — 10^ in inclement situations on the Central 

 European mountains, and the evergreen leaves of these woody plants become cooled 

 far below the freezing point of water without suffering the slightest damage. On 

 this account the seeds inclosed in the berries and cones of the trees named bear the 

 lowest temperatures without injury, which is so much the more remarkable since 

 these seeds require two summers for ripening, and therefore must pass through the 

 severe winter of the first year in a still unripe condition. The seeds of other plants 

 also are exposed to great cold through the winter. Thus, for example, those of the 

 Laljurnum {Cytisics Laharnum) do not fall off" as soon as they are ripe, but remain 

 hanging to the sides of the dehisced pods, and as these are not detached from the 

 branches until the following spring, the temperature of the seeds during the winter 

 falls far below zero. They nevertheless maintain their germinating powers. 

 Laburnum seeds, which had been during the winter for weeks under the influence 

 of a temperature of —15°, germinated in the following summer, and so had 

 evidently suffered no injury from the cold. Other seeds, too, even from tropical 

 regions, which had been experimentally subjected to temperatures of —40', were 

 not found to have lost their germinating capacity, antl consequently their proto- 

 plasm had not been killed even by this excessive temperature. 



Since, on the other hand, it is known that the young fruits and seeds of the 

 laburnum, and still more those of tropical plants, are already congealed by lowering 

 the temperature to —2°, it follows that portions of that same plant in varioixs 



