26 THE PLANT WORLD. 



currcd extensively enough to make sueh injury appear natural. 



After the discovery of cell structure in plant tissue De Bufifon 

 and Du Hamel were about the first to present a definite theory of 

 ice-formation, and consequent death. To them death seemed due 

 to the formation of ice within the cells. Since water when chang- 

 ing" to the solid form increases in volume, it seemed to them fair to 

 suppose that the cell-sap would, on freezing, increase in the same 

 way, thereby stretching the cell-walls until they ruptured. It was 

 supposed that the Huid from the ruptured cells flowed together 

 and froze as one piece. Only in this way did it seem possible to 

 account for the large ice masses found in frozen potatoes, beets 

 and other thick succulent material. ?\lany other investigators 

 since that time have held the same view, among whom were Hales, 

 Miller, Stromcr, Sennebier. Thonin. Sprengel and Schubler. 



Goeppert" in 1830 seems to have been the first to point out that 

 in some cases ice forms in the intercellular spaces instead of 

 within the cell. Sachsf in i860 showed that it forms almost 

 always in the spaces. Sachs and Nageli| both showed that the 

 expansion caused by all the water in the cell would not be suf^cient 

 to rupture the wall. Nageli discovered that cells of Spirogyra 

 which had been frozen and thawed still showed some power of 

 osmotic action, which he thought could not have been the case 

 had the cell-wall been ruptured by the freezing. The relation of 

 the protoplasmic membrane to osmosis was not then understood. 

 Both Nageli and Sachs attributed the loss of turgidity accompany- 

 ing the freezing process to molecular changes in the cell-wall 

 which thev likened to the change occurring in frozen starch paste 

 whereby the paste-like nature and abilit\- to retain large quanti- 

 ties of water are both lost. This was an important comparison 

 and holds good even now if protoplasm is substituted for cell-wall. 



* Goeppert. Ueber die Warmeentwickelung in derm Pflanzen, deren 

 Gefrieren, und die Scluitzmittel gegen dasselhe. Book 1830. 



t Sachs. Krystalll)ildung Krystallbildungen bei dem Gefrieren und 

 Veranderung der Zellhaute bei dem Aufthauen saftiger Pfianzentheile. 

 Bericht. u. d. Verhand. d. Kon. Siichs. Gesell. d. Wiss. zu Leipzig, Nat. 

 Wiss. Klasse, 12: 1-50. 1860. 



t Nageli. Ueber die Wirkung dcs Frostes aut die Pflanzenzelk-n. Sitz. 

 der Konig. baycr. Akad. d. Wiss. Miinchen, r: 264. i86l 



