5T4 



Even the same day, he noticed newly produced brown spots on some of the 

 older leaves. Later these leaves got a "glassy, dark appearance, hung 

 down and dried up." The young leaves did not suffer. The same kind 

 of discoloration and wilting phenomena were observed in other similar 

 experiments and are in all essentials the characteristics which have been 

 given by practical growers as a result of taking cold. Moebius emphasized 

 that no formation of ice in the tissues can be concerned here. 1 can bring 

 proof of this in an experiment which I made with Begonia ariiyrost'ujma. 

 A pot of this plant was taken from a warm house and put out of doors 

 after the temperature had risen to 0.5 degrees C. Within a short time, I 

 saw glassy spots appear on some leaves. 



According to the experimental results given in different places in the 

 present chapter, I perceive in the wilting and glassiness of different leaves, 

 with sharp falls in temperature the results of sudden differences in tension 

 in the tissue. The contraction of tiie cells as a result of the excessi\e cool- 

 ing will cause, in places, an outpressing of water into the intercellular spaces. 

 Besides this, the dift'erence in the diff'erent tissue forms united in the leaf 

 organ makes itself felt. We will refer in this connection to the subsequent 

 section on frost blisters where various elevations of the epidermis and loos- 

 enings of the tissue are described. 



The practical grower at any rate should kecj) in mind llie fact that, in 

 transporting plants from warm houses, there is a possibility of taking cold, 

 even if plants are exposed only a few minutes to a freezing temperature. 

 Since a sharp change of temperature should be avoided, the wrapping of the 

 pots with cloth or paper must be recommended for all cases. 



B. SPECIAL LMSTANCES OF FROST ACTION. 



TuRNiNc Sweet of Potatoes. 



In the well-knf)wn phenomenon, that potatoes turn sweet when suii- 

 jected to slight degrees of frost, Goppert^ and Einhof- had noticed that in- 

 dividual dift'erences make themselves felt. Under the same conditions only 

 part of the tubers turned sweet and remained soft, while the others became 

 hard. If the potatoes were brought quickly into considerable cold (about 

 10 degrees) they were frozen, as a whole, without showing any formation of 

 sugar. The turning sweet could not be observed except at temperatures 

 which lay only a little below the freezing point. Miiller-Thurgau found 

 that this change set in only in potatoes which had been taken from the soil 

 at least a month earlier. It could not be produced in freshly harvested 

 tubers. Probably similar phenomena led Payen" to the conclusion that even 

 before the action of the frost, the tubers, which showed the formation of 

 sugar, might have started to grow again. 



1 "Warmeentwickluiifr, p. 38. 



- Neues allgem. Journ. f. Chemie. Berlin 1805, p. 473. 



3 Cf, Czapek, Fr„ Biochemie der Pflanzeen. Fischer, Jena, Part 1, p, 371. Here 

 also notes on older literature, 



