144 



MiilK'r-Tlmriiaii (ISSli) sliidicd llic (h'posilion of ice in 

 llu' jiilci-ct'llulnrs hy llic following' procedure. He sec- 

 tioned ^vitll a eooled knife pieces of frozen tissues, snch as 

 beets, potatoes, dahlia tubers, etc., took out the little lens- 

 shaped pieces of ice located between the cells and exam- 

 ined them on a cooled slide. These ice masses consisted 

 of two layers of ice pillars {cf. Fig. 14). Each pillar was 

 a more or less regular six-sided ])rism. Within the indi- 

 vidual i)illar, bead-like air-bubl)les extended along the axis. 

 The ice masses were of enormous size as coni])ai'ed with 

 that of the cells. The cross section of the individual crys- 

 tals was itself larger than that of the cells. The length of 

 the columns was about the same in the two adjacent layers 

 except if the ice mass had been formed near the external 

 surface of the tissue, then the layer on the external side 

 was thinner. 



The surface freezing in compact ice crusts, as described 

 before, is considered by this author as the limit in the 

 series of forms that the ice masses take when they origi- 

 nate at points gradually nearer the outside surface. The 

 formation of ice between the base of the petioles and the 

 stem, described by de Mohl in his study of the fall of the 

 leaves after a frost, is also considered a particular case 

 of the same phenomenon. 



As to the question of intercellular or intracellular freez- 

 ing, Miiller-Thurgau noted that a direct examination of 

 sections of frozen tissues under the microscope shows the 

 crystals between the cells, not in them. 



Repeating an experiment previously made ])y Sachs, he 

 determined the residue left after evaporation of 21.08 

 grams of ice collected inside of a cow-beet, and found 0.04 

 g. It was, therefore, practically pure water which tiltered 

 out through the cell walls during freezing. 



^^liiller-Thurgau, described also ice masses of columnar 

 structure in animal tissues, for example, around the ali- 

 mentary canal of an earthworm left to freeze in the ground, 

 at -6°.^ 



7. Cells. Surface Freezing. Moliscli (1897), exposing 



