Excerpt from Abscission of Flowers and Fruits in the Solanaceae, With Special Reference to Nicotiana: A Thesis Submitted in Partial Satisfaction of the Requirements for the Degree of Doctor of Philosophy at the University of CaliforniaAlthough it is a matter of common observation that many plants are capable of detaching portions of the body, the underlying cause and the actual mechanism which bring about such separation are only slightly understood. The process has often been described as' One Of self-pruning by which the plant rids itself of useless portions of its body. Since abscission is sometimes confused with exfoliation, it seems desirable here to distinguish definitely between these two phenomena. It can be said that, in general, exfoliation is preceded by drying and death of the part to be cast off and that actual separa tion of the organ is accomplished by a mechanical break through dry, dead tissues. Abscission, on the other hand, is usually not preceded by drying and death of the organ concerned and its detachment is accomplished by a separation along the plane of the middle lamellae of active living cells.Abscission may be either axial or lateral. Axial abscission includes the abscission of portions of stems, shoots, entire ¿owers or fruits. Lateral abscission includes the abscission of leaves, petioles, sepals, petals or styles. Considerable attention has been given by investi gators to the abscission of ¿owers because of the theoretical detriment to crops caused by the fall of the ¿ower before the fruit is formed.About the PublisherForgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.comThis book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully, any imperfections that remain are intentionally left to preserve the state of such historical works.