HEAT. 141 



will perish in an atmosphere of thirty-two degrees, and annuals 

 are destroyed by the first frost of autumn. The manner in 

 which cold operates in the destruction of vegetables has of late 

 excited considerable interest. The long prevalent opinion has 

 been, that the well-known phenomenon, that water at the mo- 

 ment of its conversion into ice expands, was the cause of their 

 destruction. The tissues being filled with sap, it was supposed 

 that when this was frozen the consequent expansion ruptured 

 the tissues, and unfitted them for any longer performing their 

 functions. This very plausible theory, it seems, has been entirely 

 set aside by some, but by others it is still considered a concur- 

 rent cause in the destruction of some vegetables at least 



The following is compiled from an article in the 39th vol. of 

 Silliman's American Journal of Science, from the pen of Prof. 

 Lindley. 



270# " Mr. Gceppert denies that the laceration of tissue takes 

 place in freezing, and asserts that cold operates in destroying 

 the vitality of plants, which is followed by a change in the 

 chemical constitution of their juices." 



Prof. Morren has given the following conclusions as the result 

 of his inquiries : 



1. "That no organ whatever is torn by the action of frost, 

 except in very rare cases when the vesicles of cellular tissue give 

 way, but that the vesicles of plants are separated from each 

 other without laceration. 2. That neither the chlorophyll, the 

 nucleus of cells, elementary fiber, amylaceous matter, raphides, 

 nor the various crystals contained in vegetable tissue, undergo 

 any alteration, unless perhaps in the case of amylaceous sub- 

 stances, which, in some cases, are converted into sugar, no doubt 

 in consequence of the action of some acid, formed by the de- 

 composition of the organic parts. 3. That the action of frost 

 operates separately upon each individual elementary organ, so 

 that a frozen plant contains as many icicles as there are cavities 

 containing fluid ; the dilatation thus produced not being suffi- 

 cient to burst the sides of the cavities. 4. That such dilatation 

 is principally owing to the separation of the air contained in th» 

 water. 5. That this disengagement of air from water, during 

 the act of congelation, is the most injurious of all the phenomena 

 attendant upon freezing; introducing gaseous matter into organs 

 not intended to elaborate it, and bringing about the first stage 

 in a decomposition of the sap and the matter it precipitates ; so 

 that with a thaw commences a new chemical action destructive 



How is it supposed frost acted ? — 270. What is the opinion of Gceppert I 

 What are the positions of Morren ? 



