1887.] The Fructification of the Carboniferous Catamites. 389 



Since the degree of concentration of the solution greatly affects the 

 electromotive force of the metal, and since in the act of deposition of 

 a metal from its solution the concentration of the liquid around the 

 cathode is reduced, owing to slowness of diffusion, it follows that in 

 electrodeposition the counter electromotive force at the cathode will 

 vary with the rate at which metal is being deposited, and will, 

 therefore, vary with the current- deusity employed. And since, more- 

 over, the variations in electromotive force due to differences of con- 

 centration are greater for copper than for zinc, it follows that in the 

 deposition of brass from a mixed solution of cyanides of a medium 

 concentration in which zinc is slightly more electropositive than 

 copper, there will be a certain density of current with which the 

 metals will be deposited in nearly equal quantities, whilst for weaker 

 current-densities the less electropositive metal will be deposited in 

 excess, and for stronger current- densities the more electropositive 

 metal will be deposited in excess. 



Hence to variations in the concentration of the electrolyte near the 

 cathode are due the departures, observed with all currents except 

 weak ones, from the law that out of a solution of mixed metals the 

 least electropositive is deposited first. 



XIII. "On the true Fructification of the Carboniferous Cala- 

 mites." By William Crawford Williamson, LL.D., F.R.S., 

 Professor of Botany in the Owens College and the Victoria 

 University. Received May 17, 1887. 



(Abstract.) 



The true systematic position of the Carboniferous Calamites has 

 long been a debateable subject, owing to the lack of satisfactory 

 evidence respecting the character of their fructification. Some years 

 ago, Mr. Carruthers and the late Mr. Binney expressed their con- 

 viction that Calamostachys Binney ana stood in that relationship to 

 Calamites, a conclusion which the author was unable to accept; but 

 in 1869 he obtained a fragment of a new Cryptogamic fruit, of which 

 he published an account in the ' Memoirs of the Literary and Philo- 

 sophical Society of Manchester.' The central axis of this Strobilus 

 presented so many details of structure hitherto seen only in Calamites 

 as convinced the author that it was the true fructification of these 

 plants. 



Many years elapsed before a second example of this interesting 

 fruit was discovered, but seven or eight specimens of it recently 

 found in a nodule from near Oldham, have come into the author's 

 possession ; these examples are in a sufficiently excellent state of 



