34 THE PLANT WORLD. 



The cells toward the periphery of the beet or potato gradually 

 become smaller and therefore less rich in water, which in turn 

 is more strongly held by imbibition. Therefore, in an ice clump 

 lying half way from the center to the outside, the water is more 

 available on the inner side, and still farther out the difference 

 is still more pronounced. Near the outside only a few cells inter- 

 vene between the ice mass and the surface of the organ, and these 

 are small, while on the inside all the Ikrge cells tiitough to the 

 opposite side are available. The presence of other ice masses 

 seems not to greatly disturb this relation, but simply to reduce 

 the size of the remaining ice masses in the vicinity. The above 

 conditions obtain typically only when the organ is frozen very 

 slowlv. Rapid freezing tends to produce amorphous masses of 

 smaller size, and then occasionally within the cell. Sometimes 

 a few spaces are found entirely filled with ice which shows no 

 crystalline structure even though the cooling was gradual. Prob- 

 ably in these cases the spaces were filled with water before 

 freezing began. 



For observing the ice masses in frozen tissue the writer has 

 found the following a very good method if one does not mind 

 the cold. Place a table, microscope, razor, slides, cover glasses 

 and a small vial of cedar oil out of doors when the temperature 

 is low (15° F. or lower). Make free-hand sections of the frozen 

 tissue and mount in the oil. When observed through the luicro- 

 scope the location of the ice masses and their structure can be 

 seen very easily. Then, if the slide is carried rapidly to another 

 microscope in a warm room the thawing and sponging out of the 

 tissue may be observed as the water is drawn back into the cells, 

 if the tissue is a " hardy " one. The water is not drawn back into 

 the cells to any extent in delicate tissues which are killed by the 

 freezing. The writer used this method one winter in the study 

 of the ice relations within the buds and twigs of about thirty 

 species of woody plants with good results. The large ice masses 

 in succulent tissues may be seen with the naked eye. If frozen 

 beets or potatoes are cut in two the lenticular ice masses may be 

 picked out with a needle. 



The water of which the ice crystals are composed is almost 



