Sorry for being a bit sloppy and thanks for the corrections. I got the previous command I posted from another thread, which was addressing only changing tick mark labels, but it changed all fonts (xlabel, ylabel, legend and tick marks to 24. Thus, I inadvertently found some lines that did what I want, but did not fully understand them. It seems that all I ever needed was the command:
set(gca,'fontsize',24),
which does set the defaul font size for the current axes. If issued before I label, I can change other text elements without affecting the default, e.g.:
set(gca,'fontsize',16),
ylabel('y')
xlabel('x')
legend('series 1','series 2', 'series 3','series 4','FontSize',24)
changes the font sizes of everything, but the legend is font size 24, which is as much control as I hoped.