Jim Murphy has made the obvious point that it makes no sense for the SNP to ask English voters to vote against Labour if they really want to see a Labour government. The public position of Nicola Sturgeon is that she thinks English voters should vote Green, but anyone who considers that for few moments knows that the effect of that suggestion is to maximise the possibility of a Tory government.
I suspect that is precisely what Nicola Sturgeon wants. Her more minor reason for the move is to sideline the Green Party in Scotland, something that the English Greens seem all too eager to help the SNP with. If I were a Scots Green I would feel utterly betrayed by my colleagues south of the border.