The macrophytic vegetation ofthe beds and banks ofsomc st7.eams which flow into river Tormes has been studied. The abundance of each species was estimated with a scale of discrete value . The data-set obtained, was analyzed by means of the Sorensen's similarity indcx thus establishing groups ofsimilar sample unitsThe acuatic vegetation is mainly influenced by the currenc peed, probably through is effects on the substratum particle size. It has not been observed, in constrast. any influence of the che ical composition of the water. The coniposition of the bank vegetation. on the other hand. depends principally on the terrestrial c. oody vegetation which predominates in the surroundings.

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EL CICLO DEL POTASIO EN DEHESAS DEEl potasio es el elemento que se transfiere en mayores proporciones a través de frutos y de material herbáceo, que son materias altamente digestibles. Por ello, su transferencia al subsistema herbívoro es mayor que para los restantes nutrientes.El potasio es también el macronutriente más intensamente extraído de los tejidos vegetables por el agua de lluvia.Todo ello hace al potasio muy móvil y con intensas tasas de circulación a través del ecosistema. THE POTASSIUM CYCLE IN QUERCUS ROTUNDIFOLIA AND QUERCUS PYRENAICA .DEHESAS • SUMMARYA study was made of the potassium cycle in Quercus rotundifolia Lam. and Quercus pyrenaica Willd. dehesa ecosystems in the province of Salamanca, Spain.Potassium was seen to be the element whích was transferred in the greatest proportions through the fruits and herbaceous materials: these are highly digestible. Accordingly, the transference to the herbivore subsystem is greater than that of the remaining nutrients.(1) Dpto.