The report contains a study of the changes of the leaf joint which leads to dropping of the leaves. It was known that leaves that only develop toward autumn can withstand cold better than those that develop in the spring. Further leaves also fall off in frost-free climate and in green houses. Therefore another explanation must be forthcoming to account for this. A second cause of leaf abscission must be present, it may be probable that leaves stop growing because of water evaporation, whereas the stem continues to thicken which caused a mechanical mismatch between the leaf and the stem. This then would rupture the fiber which connects the stem and leaf.
Trans. of Botanische Zeitung (Germany) n1 p1-11, 6 Jan 1860.