ICE IN PLANT TISSUE. 



29 



potatoes, etc.. wlien presenting- a moist cut surface, became coated 

 with an ice crust exactly similar to that produced on soil, hut only 

 when protected from evaporation ( V\g. 4, C). Ex]Dosed tissue 

 usually produced no prisms at all. Good crusts were formed only 

 when the fall of temperature was very gradual, and in such cases 

 the prisms often reached the length of several millimeters — always, 

 of course, with one end closely applied to the freezing tissue. 

 Large artificial or abnormal chambers in turnips, etc., also became 

 lined with a similar crust. In the interior of each prism was 



Fig. 4. Diiigrammalic reyresenia'uon of ice-masses produced on or 

 within frozen beets, potatoes, etc. A, in tlie interior. B. near the periph- 

 ery. C, on a freshly cut surface. 



ustially a chain of minute air bubbles lying longitudinallv near the 

 axis. These probably came from air dissolved in the cell sap and 

 separated from it in the process of freezing. On melting, these 

 bubbles remained in the water for a long time undissolved, thus 

 forminc' a sort of foam. 



