into a cold place, rcmaiiicd alive. TVom this, it is c\ idenl that the rapid 

 thawing and not the frost is the cause of death. 



Miiller-Thurgau has stated of ripe fruit and Molisch of the leaf of 

 Agava americana, that these objects can be kept alive after moderate freez- 

 ing, if thawed very slowly, but that they die when thawed rapidly. 



I pressed the surfaces of the frozen leaves of herbaceous Cinerarias 

 between my finger tips. The plants, left in their places of growth, showed, 

 ^fter thawing, that only the places pressed with the fingers were killed. 

 According to the discoveries of gardeners, it is only the tender-leaved, juicy 

 spring blossoming plants, grown in greenhouses (Cinerarias, herbaceous 

 Calceolarias, etc.), which, after a night of freezing, can be rescued by the 

 longest possible retardation of the thawing. 



In plants perfectly resistant to ice, however, the rate of freezing and 

 thawing seems to have but little influence on life. 



In explanation of the matter, two points should be taken into consid- 

 eration. First, in rapid thawing, the same processes will be enacted which 

 occur, for example, in the evaporation of fluid carbon dioxid whereby the 

 formation of solid carbon dioxid takes place, as is well known. In rapid 

 thawing, the warmth necessary for melting will be removed, not only from 

 the surrounding air, but also from the deeper layers of this part of the plant, 

 which are thereby cooled down still more. In such plants in which the 

 critical point, i. c, the specific minimum, lies close below the freezing point, 

 this removal of heat, increased by rapid thawing, can cause death. 



The second point to be taken into consideration is that the cell wall, 

 from which ice has been crystallized, cannot possibly soak up the great 

 amounts of water which are produced suddenly by rapid thawing. The 

 water remains in the intercellular spaces and evaporates there while the cell 

 of the leaf is not able to regain the necessary turgid condition. From this 

 comes the gardening method of protecting from the rising sun all i)lants 

 which have sufifered from late frosts. 



Let us consider finally the natural processes of the autumnal changes 

 of material from the standpoint of Mez's theor)' as here discussed. When 

 the plants prepare for winter, they collect the greatest possible amounts of 

 reser\'e substances and reach the maximum at different times, according to 

 their individuality. In Plniis ansfriaca, for example, Leclerc du Sablon^ 

 found this maximum in May, but in the spindle tree (Evonymous Euro- 

 peus), which sends out its shoots earlier, he found it in March; in decidu- 

 ous trees the maximum is reached in the fall. In evergreen plants, the 

 reserve carbo-hydrates remain abundant in the leaves-. Their activity 

 seems reduced to a minimum, since their stomata are closed permanently. 



1 Leclerc du Sablon, t)bor die Reservekohlehydrate der Baume mit au.sdauern- 

 den Bliittern. Compt. rend. 1905. p. 1608; cit. Centralbl. f. Affrlculturchemle 1906, 

 p. 322. — Fabricius, K, Untersuchungen iiber Starke- und Fettgehalt der Fichte 

 usw. Naturwiss. Z. f. Land- u. Forstwirtschaft 1905, p. 137. 



2 Simon, Der Bau des Holzkorpers sommer- und wintergriiner Gewachse usw. 

 Her d. D. Bot. Ges. 1902, p. 229. 



