Periodical Literature. 321 



According to Wiesner the disorganization of the middle lamella 

 in the separation layer is due to reduced transpiration ; this leads 

 to oxidation of the chlorophyll, the formation of acids, especially 

 oxalic acid, and to a ferment which destroys the cells. Jaccard 

 found many oxalate of lime crystals in the mesophyll of the frozen 

 leaves, as well as in the parenchyma of petiole and ribs, but no 

 free oxalic acid. 



If the separation layer is formed before the frost, an ice layer 

 is formed in the layer and on thawing the leaves fall, even green 

 ones. The changes which prepare this leaf fall are usually 

 gradual, under the influence of gradual reduction in light and de- 

 creasing transpiration ; differently colored substances, anthocyan, 

 tannin, tannoidin and humus formations causing the discolora- 

 tion, while the starch is decomposed and wanders into the twigs ; 

 water is lost, certain parenchyma cells at the base of the petiole 

 elongate transversely and form the separation layer. 



In the year of observation warm weather prevailed until Octo- 

 ber 20, vegetative activity continuing, and frost found the foliage 

 unprepared for the fall. While the mesophyll cells were consider- 

 ably dried out, those of the petiole were turgid with water. This 

 would argue that the formation of the separation layer depends 

 on the chemical changes in the chlorophyll rather than on the 

 cessation of transpiration and assimilation. Starch was found in 

 the petioles two days after the frost, but after a fortnight had 

 it vanished, while the blades still showed undiminished quantities, 

 and it was still present by November 20 in the leaves that were 

 hanging on. It looked as if only the protoplasm in petiole and 

 midrib had been changed, and the ferments of the cellsap which 

 dissolve the starch and conduct it into the twigs had remained 

 active. The cell tissues of the petiole were still able to perform 

 osmotic processes but were unable to form the separation layer. 



The influence of frost on the protoplasm was peculiar. While 

 the color remained green much xantophyll was shown by the 

 spectroscope ; but a solution in alcohol treated with benzin did 

 not split into cyanophyll and xantophyll ; the chlorophyll had be- 

 come resistant to changes. This experience may account for the 

 finding of green moss and leaves in peat bogs and under thick 

 layers of mud. The green chlorophyll, to be sure, persisted only 

 on the upper side, where the crumpling of the leaves prevented 

 direct light influence; the under side turning brown. 



