179 



condition is obtained l)y dialysis. He attributed Ihe in- 

 fluence of tlie length of time in the frozen state to a re- 

 sulting- slow increase in the size of the particles; in 

 larger particles peptization after thawing would become 

 impossible. 



2. Tissues. The alterations caused by freezing in tis- 

 sues consist in changes in the general appearance, color 

 and consistency of the material, in a release of enzymes 

 and other substances, in some chemical transformations, in 

 a modification of the protoplasmic structure and in some 

 cytological changes. A few examples of these various 

 alterations will be described shortly, in the order given. 



Some externally observable injurious effects of freezing 

 in plants, and particularly in leaves, are well known by the 

 agriculturists. Following Goeppert (1830), who is one of 

 the earliest observers, we shall mention a blackening of 

 the surface or of the entire organ, a more fleshy consis- 

 tency, a somewhat transparent, shiny and glassy appear- 

 ance, a loss of turgor, an exudation of water and a rapid 

 desiccation. Flowers become, in general, dark browai. 



Goeppert remarked a change of color of another type in 

 some white orchids which, after freezing, become pale blue 

 and finally dark blue. This property has been used as a 

 criterion of death by several investigators in their studies 

 of injury by cold. 



Other changes in color have been described by Kylin 

 (1917) in algae. 



Molisch (1897) noted that some plants which contain 

 coumarin release that odoriferous substance on being 

 frozen. 



The release of enzymes by freezing and the consequent 

 increased enzymatic activity, in some tissues, is a commonly 

 observed fact. 



Formation of sugar under the action of cold has been 

 reported by many investigators. The literature on ^^in- 

 ter hardening in plants contains abundant data on this 

 subject. 



Luyet and Grell (1936), in centrifuging onion root tips 



