Anomalie nella Differenziazione del Legno in Rami di Olivo Defoliati a Varie Epoche

Abstract

A specimen of Olive Tree has been divided in five sectors consisting of an equal number of branches. One of the sectors has been left as a control. The second has been defoliated on Dec. 12th 1949; the third has been defoliated on January 25th 1950, the fourth on March 5rd; the fifth on March 29th. On April 3rd 1951, samples of wood and bark have been excided from the branches of each sector. The branches of sector 1 (control) were left in the normal conditions so that the cambium during the growth period of 1950 was under the controlof two sets of leaves: those of the preceeding year and those of the same year. The branches of the sector 2 passed through the greatest part of the winter and the whole vegetative period of 1950 without the set of old leaves of 1949. The branches of sector 3, passed through the first part of the winter with the leaves of the year 1949, the second part of the winter without leaves and the vegetative period of 1950 only with the new joung leaves. The branches of the sector 4 passed through the whole winter with the leaves of 1949, a brief period, from March to April with hout leaves and, the grouth period of 1950 only with the new joung leaves. Finally the branches of the sector 5 passed through the whole winter, just as late as the opening of the new buds, with the old leaves of 1949, and all the growth period of 1950 only with the new joung leaves. These branches passed no period devoided of leaves, but during the growth season of 1950 they were provided only of one set of leaves and not of two, as was the control. It is known that the life cicle of the leaves in the olive tree is biennial. The leaves unfold in the spring and persist on the branches as late as the end of the summer of the following year, so that the branches have only one set of leaves during the winter and two sets of leaves during the spring-autumn period. The whole four defoliated branches produced, during the year 1950, anomalous secondary wood. The secondary wood produced during the year 1950, in the four defoliated sectors, consists of two or three false rings, the whole of them do not equal the width of the last false ring produced by the control branches. The abnormalities of the wood produced by the defoliated branches deal above all with fibers. Vessels and parenchima are interested in a lower degree. The vessels of the defoliated wood are more uniform and slightly narrower than those of the control, often irregularly grouped, they have thin walls. Their frequency per surface unit is about twice that of the control (see Table 1). This high frequency depends upon the scantiness of the interposed tissue (fibers) in which they are immersed. The parenchima is uniformously aboundant in the whole wood tissue. The starch appears to be in the same quantity in both kinds of wood (control and defoliated). The fibers are scarse in the defoliated wood. They are differentiated in thin layers at the end of each ring, and are permeated with parenchima cells. The fibers of the control have charcteristic toothed sharp ends, while those of the defoliated wood have thin and smooth ones. The number of the false rings (poussées) changes in the defoliated woods according with the date of defoliation, increasing from the early to the late defoliations. The fiber layer at the end of each false ring, in the defoliated branches, is very thin in the early defoliated branches and rather thick in the late defoliated ones. In the late defoliated branches, the fiber layer is thicker at the end of the first false ring, becoming thinner in the following ones, so that it almost lacks at the end of the last one. The present experiment shows the importance that have the mature leaves (one year old) to determine a normal composition of the secondary wood. The one year old leaves play their role also during the winter, as the abnormalities in wood histology decrease in the branches defoliated late in the winter. The leaves elaborate problably a specific stuff controlling the differentiation expecially of mecanic tissue, which accumulate in proximity of cambium, so that this stuff is easily available at the beginning of the vegetative period. The mature leaves only elaborate the fiber stuff and their activity is propably highest during the growth period.