524 



found on one side the i,M-()\\th of tliis cork-color side, containing:; tlie stone 

 cells, is often retarded, thus producing deformed fruit. 



After 1 had succeeded in causinjj a splitting of the cuticle in tough 

 leaves by the action of artificial frost, I did not hesitate to trace the injuries 

 in the wax coat of young fruit to frost action, more particularly the forma- 

 tion of such "rust rings" as had been observed only in years with late frosts. 

 The pears, which are susceptible to frost, suffer most abundantly and 

 greatly, in fact usually on one side and at a certain height on the tree. 



Thk r>i:H a\i()r of Oi.di k I'oi.iac.i'. With .A.ctjtk Frost Action. 



During frost, changes in the chlorophyll grains are noticeable inasmuch 

 as they usually round up into lumps in the cells which have become poor in 

 sap. A chemical change of the chlorophyll coloring matter, due to the frost 

 alone, is not assumed by the majority of investigators, so far as found in 

 statements concerning frozen chloropliyll solutions. \\ iesner found' no 

 difference in a chlorophyll solution in oli\e oil exposed to a temperature of 

 30 degrees C. below zero. On the other liand Kunisch- states that the 

 alcoholic extract of chlorophyll from hyacinth leaves, frozen at 7 degrees 

 below zero, was found to diff'er from that of leaves which had^ not been 

 frozen. Often dull whitish spots are found in frozen leaves which can 

 arise from ice accumulations crystallized out into the intercellular spaces, 

 Hoffmann found in Ceratonia, Laurus and Camphora, a vesicular raising 

 of the epidermis and called it a "frost blister-''. In heavy frost, the leaves 

 which have been frozen through become as brittle as glass and transparent. 

 When such leaves are thawed, the change in color depends upon whether 

 the protoplasm of the cells has been killed or not. If it is dead, it becomes 

 permeable to acids in the cell ; these penetrate to the chlorophyll grains, and 

 cause their decomposition (the formation of chlorophyllan) : the cytoplasm 

 turns l)rown ; the cell sap exudes rapidly; the leaf dries into a brittle, brown 

 mass. Ciopperf*, who describes the various colorations of foliage leaves, 

 also mentions an extremely strong weedy smell in frozen plants. In ferns 

 the odor peculiar to the whole family is retained in frozen and dried speci- 

 mens in an unusual intensity. In artificially frozen branches of the sweet 

 cherry I noticed a decided odor of bitter almond. These phenomena are the 

 result of the chemical changes which make themselves felt immediately 

 and strongly during thawing, h'luckiger' has observed a dift"erent effect in 

 the frozen leaves of the cherry laurel. During distillation, these gave off 

 an oil differing from that of the fresh leaves and no prussic acid, while 

 leaves covered with ice, but not frozen, gave both substances under normal 

 conditions. 



1 Wiesner, Die natiiilichen Erscheinungen zum Schutze des Chlorophylls, etc. 

 Festschrift d. k. k. zoologr.-bot. Ges. zu Wicn 1876, p. 23. 



- Kunisch, H., tJber die ti'.dliche Wirkung niederer Temperaturen aiif die 

 Pflanzen. Inauguraldisscrtation. Breslau 1880. 



:' Kunisch, loc. cit. p. 22. 



•* Gi'ippert, t)l)er Kinwirkung des Frostes auf die Gewiichse. Sitzungsb. d. 

 Schles. Ge.s. f. vaterl. Kultur 1874; cit. Bot. Z. 1875, p. 609. 



5 The effect of intense cold on cherry-laurel; cit. Bot. Centrall)l. 1880, p. 887. 



