Osservazioni E Considerazioni Sul Fenomeno Della Micorrizia al Piccolo San Bernardo

Riassunto

L'A. espone i resultati di osservazioni compiute sul fenomeno della micorrizia, constatando fra l'altro che esso si attenua nelle piante alpine coltivate nella Chanousia rispetto a quelle spontanee dei dintorni. Enuncia l'ipotesi che i componenti di un'associazione vegetale sieno fra loro strettamente collegati a causa del considerevole sviluppo del micelio micorrizogeno, che può passare anche dalle radicì di una specie a quella di un'altra.     

Alcune Osservazioni Sul Contenuto del Cribro in Giovani Fusti di “Guizotia Abyssinica” Cass

Summary

The area of S. Rossore is part of an old marshy plane, placed on the right side of the mouth of the river Arno and reaching the mouth of the Serchio, which untill some centuries ago flowed indipendently into the Tirrenian and only later has been diversed into the Arno.

On the dunes and downs of S. Rossore a very interesting type of Flora survives; its present physionomy going up to the Quaternary period, could be preserved till today as S. Rossore has been since a long time a private farm and a park of princes, dukes and kings.

The most interesting Flora of S. Rossore is that of the downs, expecially of the oldest ones (pleistocenic) which separated untill historic times, the open sea from the lagoon of Fasana, which penetrated just inside the present walls of Pisa.

For this reason these downs have been studied with a particular care. The floristic research have been based not only in the study of the specimens collected by the author, but also on the material of which the author could dispose. That is: the specimens of the “Herbarium Centrale Italicum” of the Botanical Institute of Florence, the data of the “Prodromo alla Flora toscana” and of the “Supplemento” by Caruel and Baroni. Altogether the taxa listed up to the present date are more than 700.

The identification of the species has been critically made, adopting the rules of the “International Code of Botanical Nomenclature”. When those rules could not be follewed an explanation has been given.

The facies of the vegetation of S. Rossore are the following: The seashores, the dune tops, the wet downs, partially flooded during the winter, and the permanent marshes.

The facies of the meso-igrophilous woodlands, growing expecially in the most encient downs, has been particularly investigated. In these stations grows a mixed wood of Quercus pedunculata, with Fraxinus oxycarpa, Fraxinus Ornus, Alnus glutinosa, etc., with many boreal-montane plants and Sphagna colonies, particularly at the edge of the partially flooded areas. In these Sphagna colonies are located some of the most exigent atlantic species (Hypericum elodes, Hibiscus palustris, etc.).

These mesophilous-igrophilous woodlands represent a relict of the vegetation pushed planewards to sea level by the glacial climate, and to its ingression is due the scarse importance that presently has here the mesophilous macchia of Quercus Ilex, as is shown by the biological spectrum of the flora of S. Rossore, (P 11, Ch 3, H 33, Cr 20, Th 22) indicating a rather scarse mediterranean character, in comparison with that of M. Argentario.

The flora of S. Rossore has a rather low degree of community (70%) with that of the “Paludi Pontine” which are only a short tract southawrd (2°1/2) and which stood the same geological events. On the other side, the lower degree of community between the Floras of S. Rossore and the Pine Forest of Ravenna (60%) which are located at the same latitude, shows the importance of the Appennines placed as a barreer between the floras of Central Italy.

In this paper has been focussed the importance that the coastal marshes can have had for the preservation of an old tertiary flora during the quaternary period. This flora in fact could be able to move, during the Quaternary, from the marches to the impending hills and viceversa, according to the different glacial phases (a tipical example is Periploca graeca).

It has been particularly pointed out the importance of the woodlands of the plane and the coastal marshes in preserving the colonies of montane or boreal-meso-philous-igrophilous species during the interglacial periods, (for ex. Narcissus poëticus, Leucojum aestivum, Menyanthes trifoliata, etc.) This phenomenon is particularly important in the marshes, situated in the lower course of the river Arno, penetrating far into the Peninsula, where they are dominated by the peacks of the Appennines and of the Apuane Alps.

From this research it is possible to argue that some atlantic species (mediter-ranean-atlantic as Erodium maritimum and Anagallis tenella and eu-atlantic as Hypericum elodes) could have spread towards the mediterranean basin along the coastal platforms, which gradually emerged above sem level in consequance of the glacial eustatism.

This migration was possible during the ascending phases of the glaciacions, when the climate was markedly of an oceanic type.

This study has been made with the aim of emphasising the opportunity of the establishment of a “National Park” in S. Rossore, to preserve his relict formation so important to testify the history of the quaternary vegetation of the mediterranean coasts, and particularly the anteclimax of the higrophilous downs, represented by the coastal “Selve”.