1), may be deeply grooved or perfectly plane; and the spore-bearing a leas, or sori, may be either continuous, completely covering both surfaces, or confined to the grooves. Millions of spores are liberated during a year, by each sporophyl. They are olive green in

In the case of electrolysis the only specific action which we have to attribute to the current is that it tends to set free the anions a t the anode and the cations at the cathode."' At the anode this action may result in the formation of new cations due to the corrosion of the anode by the liberated anions. Employing a different terminology, these facts may be expressed as the diminution of electric charges on the cations at the cathode and the increase of like charges a t the anode. The electric charges of an ion may be looked upon as the manifestation of valence if we regard valence as potential combining capacity. If we define oxidation or reduction as a change in, valence and keep in mind the theory of valence changes, from either view point it is seen that a t the cathode we have a reduction and at the anode, an oxidation.So, we may adopt as a rule that electrolysis in aqueous solution invariably leads to oxidation a t the anode ar_d reduction a t the cathode.Oxidation a t the anode may be fully explained by the simple chemical action of the discharged anion, and reduction a t the cathode by the action, likewise, of the discharged cation. Anions being electronegative in character, on being discharged at the anode they appear as strong oxidizing substances and either escape as such or corrode the anode or react with some oxidizable substance in the electrolytic bath. In an analogous manner may be explained the corresponding reduction at the cathode.In pure chemistry we understand oxidation as meaning the addition of electronegative substances, as oxygen, or the subtraction of electropositive substances, as hydrogen, and a reduction as the reverse. Since either process may manifest itself as a change in valence or the number of electric changes Bancroft: Trans. Am. Electrochem. SOC., 8, 33 (1905).

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The analogy between chemical and electrochemical reactions has been studied in considerable detail in this' and other laboratories, and many data have been collected. Many reactions commonly considered and spoken of as purely chemical are in reality electrochemical. Still there is no sharp line of demarcation. Frequently, reactions are induced by galvanic action, set up by bringing together in a corrosive medium and in the presence of the compound with which a certain reaction is desired, two metals of differing electroproperties so that an electric couple is formed. The zinccopper couple of Gladstone and Tribe may be cited as an example of such a case. This is producing chemical action by a concealed, electrochemical reaction. We can go a step farther and induce an electrochemical phenomenon in a purely chemical way-we can liberate ions which generally are set free only by electrolysis.'When sulphate ions, SO,, are discharged electrolytically against a metallic anode they do one of three things-in cases where the anode is soluble they dissolve the anode quantitatively forming sulphates ; if the anode is insoluble and the current density low oxygen is set free; or if the current density is high and also the concentration of sulphate the sulphate ions combine to form the divalent, persulphate ion, If we decompose the persulphate in the presence of an insoluble anode (or in the absence of any anode, which amounts to the same thing) we should expect the evolution of oxygen, and that we get. This may be shown by mixing, in a gas evolution bottle, concentrated sulphuric acid with a saturated solution of ammonium persulphate, containing an excess of persulphate crystals and a small amount of mans,a. Bancroft: Trans. Am. Electrochem. SOC., 8, 33 (1905). Bancroft: Ibid., 8, 43 (1905).