Relazioni Ormonali Nella Fruttificazione Delle Orchidee.: 3. Induzione Della Fruttificazione Mediante Trattamenti Auxinici

Abstract

Abstract Hormonal relations in the development of the Orchids ovary III. Induction of fructification by auxin treatments. — The author in order to assess the role of pollen and the interaction between pollen tubes and ovary in Orchids has compared the normal processes of fructification with the partheno-carpic ones induced by less specific stimulations (auxins, dead or foreign pollen). These less specific treatments have always given an initial stimulation similar to that given by normal pollen, but in some species the stimulus ceased after a few days while in others a definite growth stimulus was noticed often leading to parthenocarpic fruit ripening. Among the auxins used the most efficient one was finely powdered NAA laid on the stigma. This was probably due to the stability of this substance, its low solubility and therefore its slow flowing down towards the ovaries, which in some species require auxin for several months. The best results were had in « Cymbidium »; NAA stimulates the resumption of growth till fruit repening, the process taking 8–13 months. The counts of growth failures with dropping of the ovary in different periods seem to show that at first the growth is induced by the NAA treatment, and later by the ovules themselves; afterwards the ovules become eshausted while the pericarps remain vital for some months. Comparing the growth of parthenocarpic fruits with that of normal ones it seems possible to conclude that in the course of normal fructification there is first of all a stimulation due to the auxins contained in the pollinia, then a growth of the placentae supported for some months by a regulator produced in the ovaries by the pollen tubes and later by growth regulators formed by the placentae themselves. At about the sixth month fertilization occurs and probably the further growth of the ovules into seeds is autoregulated. During this period the developing seeds affect also the growth of the pericarp. If instead of the stigma cuts made in the column or, in some species, in the ovary were treated the result was the same. From this fact one may deduce that in such species neither the stigma nor the column plays an essential role in the fructification process. The behaviour of the different genera seems to show that throughout the Orchidaceae, as in other families, the regulation of the fructification is not uniform. The author relates for some species on the inception time of some normal embryological stages, as these data may be useful for future researches. The relevant literature is briefly reviwed.