Are there guidelines for amount and content of text in figure captions for theses? In writing my thesis in geosciences I have a number of figures with a fair amount of text content. Is there some limit I should adhere to -- say for example max 5 lines -- before I should just write 'refer to text'? 
A related question is where citations should go, especially in the case of several needed for one figure (e.g. a plot of n sets of data from n different sources). Again, is there some point where I should say refer to text for citations?
I would imagine this may vary from field to field, but in the biological sciences the caption text in journal publications is often verbose to the point of absurdity. That being said, I would simply use common sense; If the description takes more than a paragraph, you should definitely "refer to text". Generally speaking, the caption is simply a textual guide as to how to read the plot, with (maybe) a sentence drawing the reader's attention to a particular feature of the plot. It should mostly describe the plot, and only sparingly discuss it.