Hi
I have observed some data in the form of X-->Y.actually it's a cline that represents the dispersal of a plant in proportion to the height of an area.I need a TEST to recognize whether there is a logical relation between my observations or not.e.g. while the height is increasing is the dispersal decreasing steadily,exponentially or with a determined acceleration?
thanks

Well there are many ways you can do that.
First is, plot them in Excel and see fit the trend line using line properties. It will provide you multiple option for fitting the data set, e.g. linear, exponential, log etc. It also provide you the equation of the line of best fit, which will tell you the data trends.
Second thing you can do is, look into any basic statistics book. There are many tests to see see if X and Y are correlated or not? But requirement for second option is larger data set. IN order to get significant difference, you would have to have a larger sample size.
Third: You can perform some sort of optimization/simulations, but major task in this is you have to define your target function, something what you have mentioned as 'Logical relation' in your post. You have to define that relationship in numerical form.

You can find many other tests to see what you looking for; however, I think, first choice is the best one. Plot your data, fit a line of best fit, get an equation and see if it has an increasing or decreasing relationship. Hope this helps.