[JMP 9] - question on diff. in slopes

How do I check to see if 3 seperate slopes are significantly different or not in JMP? I am using the X by Y analysis plotting radiation intercepted and biomass accumulated for soybean for 3 different planting dates. I group by planting date and get 3 curves on my graph. I need to know how I can see if the slope of each line/slope is sig. different fromt the other two. Is the x by y platform the correct one to use? Thanks.