FKEEZING ANU IICUNING. 539 



walleil tissues is prevented l>y this position, ami iluring the night the vertical 

 position of the young leaves lias this advantage, that by it radiation, that is to 

 sjiy, excessive loss of heat, is hindered. The young not yet completely developed 

 foliage is in both these respects very sensitive, much more so than adult foliage, 

 and this depends upon the fact that the latter is comparatively poor in watery 

 contents, and the composition of the protoplasm has become altered. It may 

 happen that in the same plant, under the same conditions of habitat and like 

 conditions of temperature of air and soil, while the young leaves perish after 

 bright nights in consequence of too great loss of heat, the fully-developed leaves 

 sutler no injury. This brings us to the question, Wherein the damage to plants 

 caused by great loss of heat actually consists? 



FREEZING AND BUKNING. 



Pancratius, Servatius, and Bonifacius, whose names stand in the calendar 

 against the 12th, 13th, and ]4tli of May, have popularly been called " Ei.smanner" 

 in southern Germany and Austria. They have received this nickname on account 

 of the fall of temperature which takes place every year about the middle of May, 

 the cause of which is not yet fully explained. Later in the summer such falls in 

 temperature, connecteil with cooling of the atmosphere on a lai-ge scale, occur on 

 certain days with some regularit}-; but the.se have not received so much notice 

 because they are not so dangerous to field products, fruit and wine, as the relapses 

 about the middle of the month of May. Moreover, although really cold days occur 

 ill .lune or July, they are never followed by a frost, while the three "Eismanner" 

 of May usually bring with them severe frosts at night, even in the mildest regions 

 of Central Europe, thus doing incalculable mischief to vegetation. 



What first of all strikes us in a frozen plant-organ is that it has completely 

 lost its elasticity. On liending and pressing back with the finger the frozen, 

 stiffened foliage-leaf, a permanent fold is immediately produced; the leaf is broken 

 along this fold, and can no longer resume its former position. At the time of 

 breaking a noise is heard like the crushing of pounded ice, and as a matter of 

 fact it is actually crystallized ice formed in the interior of the leaf which is 

 broken by the pressure and causes this crunching to be heard. As the tempera- 

 ture rises during the day, the frozen plants become thawed, but most of them 

 retain no longer the elasticity whicli they possessed before the frost. The leaves 

 hang down flaccidly, are of a difierent green, and are more transparent than 

 formerly. The surface is damp, and the epidermis is easily detached from the 

 deeper tissue -layers. Gradually the languid leaves shrivel up, become dried, 

 and assume a brown or blaek colour, 'i'liey entirely resemble burnt or charred 

 leaves, and the farmer says that the frost has bui-nt them. 



What takes place in the interior of the plant on account of this freezing? 

 Tlie idea which botanists once held is as follows: the watery cell-sap of the 

 plants stiffens to ice; but the ice takes up a larger space than was occupied by 



