519 



is oxydized to indigo. Prillieux^ states that this change appears first with 

 thawing. Other statements on the behavior of the coloring matter in blos- 

 soms vary as greatly and it can only be said in general that the red coloring 

 matter is one of the most resistant ; in fact, according to Goppert'-, who has 

 collected many observations on the color phenomena produced by frost, it 

 can be increased in the leaves and blossoms with slight frost action. 



Most frequent, and therefore most important, are the disturbances in 

 the blossoms of our fruit trees due to frost. For all practical purposes, the 

 way the process of discoloration takes its course is immaterial. Scien- 

 tifically, however, it may be of interest to become more exactly acquainted 

 with the frost action. But since it is impossible to determine in natural 

 spring frosts what are the first effects and what the subsequent changes, I 

 have subjected apple blossoms to artificial frost. 



After a blossoming apple branch had been exposed for 2 hours to a 

 temperature of 4 degree C. below zero, the investigation, carried on imme- 

 diately after the removal of the freezing cylinder, showed that all the petals, 

 and also some places in the leaves, had taken on a glassy consistency. 



Even after a few minutes (the air temperature was 11 degrees C.) 

 a flabbiness and a turning brown began in the parts which had become 

 glassy. The brown discoloration of the leaves, therefore, is not the direct 

 effect of the cold but a phenomenon making itself felt first with thawing. 

 The petals, with the natural reddish tinges on the under side, had brown 

 veins and were spotted. The edges began at once to collapse and dry up. A 

 cross-section showed that the discoloration was due less to the turning brown 

 of the cell walls than to that of the cell content, since these excreted reddish 

 yellow to brownish yellow solid masses deposited usually in the longitudinal 

 axis of the cells and resembling carotin. The different cell layers of the 

 petals behaved differently. The excreted yellow masses could be proved to 

 be especially abundant beneath the colorless epidermis which had remained 

 at its natural height. Besides this, the parenchyma cells which accompany 

 the vascular bundles of the fine veins showed these excretions especially 

 distinctly. This latter circumstance caused the venation of the fine petals 

 to appear strikingly brown to the naked eye. With the rapidly advancing 

 process of drying, the cells of the mesophyll collapsed, wdiile the cells of the 

 epidermis retained their natural size. 



Fig. 103 shows a part of a petal soon after it had been removed from 

 the freezing cylinder. It shows the leaf still in its natural dimensions, with 

 the large intercellular spaces (/) between the very thin walled cells of the 

 flesh and with the unchanged epidermis (c). The discoloration, due to the' 

 yellowish brown contracted mass of the cell content (b), is most intense 

 near the vascular bundles (g) and in fact especially so on the under side of 

 the leaf. In the vascular bundle the narro\N- spiral ducts have turned brown. 



1 Bot. Zeit. 1871, No. 24.— Bull, de la Soc. bot de France 1872, p. 152. 



2 Kunisch, H. tJber die todliche Wirkung- niederer Temperaturen auf die 

 Pflanzen. Inauguraldissertation, p. 29. Breslau 1880. 



