Tex : size and position

Hello,

I'm making simple plots with matplotlib, and I've tried the mathematical
text stuff, but

ylabel(r'$\alpha > \beta$')

puts the text horizontally instead of vertically. Also, I don't get any
effect using fontsize :

xlabel(r'$\alpha > \beta$',fontsize=20) or xlabel(r'$\alpha >
\beta$',fontsize=10)

give the same thing.

Thanks,

YLD