142 



Tliouars described ice formalioiis in llic pilli and in tlic 

 cortical parenchyma of the stem of some plants (vine, 

 elderberry, etc.) The ice crystals were occasionally so 

 abundant that it was ])ossible to obtain a dish-full of them. 

 In somi' instances thei-e was a com})lete cylinder of ice 

 below the cortical layer. On meltin^u', tlie ice coHected in 

 tlie tissues i^ave almost clear water. 



Later de Mohl {op. cif.) discovered that, wlien the leaves 

 fall after a freezing weather, a layer of ice can be seen at 

 the base of the petiole, separating the leaf from the branch. 

 The mechanism of the formation of this ice layer is prob- 

 ably the same as that of surface freezing of stems dis- 

 cussed above. 



Caspary {Bof. Zeituug, 1854, p. 665) who had observed 

 surface freezing on various plants, in the Schoeneberg 

 garden, near Berlin, described also the formation of 

 masses of ice in the interior of fresh stems, in particular, 

 below the epidermis. He attempted an anatomical study 

 of the tissues from which the ice originated. But he says 

 that he could not ascertain whether the separation of the 

 cortex from the wood and of the wood from the medulla 

 was accom])anied by a tearing of the cells or if the latter 

 Avere only pushed apart. 



Several observers, however, after Goeppert (1830), have 

 pointed out that the cells, in frozen tissues, are not torn by 

 ice crystals. Such an observation, together with that of 

 the presence of ice in the intercellular spaces, contributed 

 to estal)lish the notion that water does not freeze in the 

 cells but that it is withdrawn from them during the freezing 

 process. 



Sachs (1860, vf. also his "Textl)ook of Botany," Book 

 HI, Ch. Ill, Sect. 7), by cross-sectioning leaf stalks of a 

 frozen artichoke, observed that the epidermis ^vas separ- 

 ated from the parenchyma by a layer of ice, and tliat the 

 parenchyma itself had split into several ])ortions separ- 

 ated from each other by ice (Fig. 13). From pieces of 

 leaf stalk weighing 396 grams he picked out as much as 

 99 grams of ice. This ice was almost pure water; after 

 evaporation it left only 0.1 'r of solid substance. 



