BOTANY. 779 



(2) the fact that these parts have, during- the previous growth, been 

 daily receiving extra sunshine and have tliereby become more turges- 

 ceut than the shaded portions. This lias prepared their cells to suffer 

 more from frost. Kunisch likens tlie chemical change that the sap 

 undergoes in each cell to the freezing out of cryolites at specific tem- 

 peratures from ordinary solutions; it is the chemical change that is the 

 real cause of the death of the cells, and if too many cells are killed 

 the whole plant succumbs. Moll shows that the wilting of the frozen 

 leaves is due to the collapse of the cells whose exuded water has frozen 

 in the intercellular spaces. 



Sorauer traces the frost brand or blight, the frost Icrebs or cancer, 

 the frost heulen or boils, the frost Jeppen or patches, and the frost 

 runzeln or wrinkles and puckers to a healthy effort of the plant to get 

 rid of or cover up the cells that have been killed by the frost. 

 When a plant is abundantly supplied with warmth and moisture it 

 suffers most from spring frosts; but when it has been retarded in its 

 development, and especially when it is still in its winter stage of vege- 

 tative repose, it suffers least. When the autumn and early winter are 

 warm and dry and the tree continues its growth late in the season the 

 subsequent winter freezes are more injurious to it because in general 

 there is more sap in its cells and more cells suffer from the chemical 

 changes produced by the cold. U. Goethe collects a number of facts 

 illustrating this general principle. He recommends that all frost wounds 

 be cut out as soon as perceived and closed up with grafting wax; cov- 

 ering the wounds M'itli clay may sometimes do, but in general fungi 

 develop beneath that. The hot wax or wash with fungicides may kill 

 the wood to the depth of a millimeter, but it preserves the rest. Goethe 

 recommends to strip off the leaves in autumn, to loosen the earth about 

 the roots, to whitewash the branches and trunks with lime and 

 envelop them with straw. Sorauer has esijecially investigated both 

 the mechanical and chemical injuries and the effects of temporary 

 frosts and of long-continued freezes. Miiller-Thurgau in 1886 snmmed 

 up the exi)erience of others and the thousands of experiments made by 

 himself about as follows: The exudation of the sap from the cells and 

 its freezing outside is the death process. Then the injury is done, the 

 cell is dead from that time forth, but perhaps not the Tvhole plant; no 

 process of thawing will revive the dead cell or dead plant. As a pro- 

 tection against loss by frost he suggests: The proper selection of vari- 

 eties which, in <-onscquence of their origin, can be considered as able 

 to resist frost; the new development of hardy varieties from such 

 hardy individuals as may l)e occasionally discovered; the diminution 

 of danger against frost by proper (;ultivation and nourishment and 

 whatever makes the plant sound and vigorous, as suggested by the 

 various exi)eriences of severe winters; the acceleration of the begin- 

 ning of the period of vegetative rest (stripping the leaves is considered 

 to be without advantage) and the retardation of development — that is 



