Understanding a dendrogram (no cursework)

[hexa]

Hello,

I tried to find a fitting forum but did not quiet succeed. The following diagram is an example of something I've been given at work. I try to understand it but fail with that.
http://img98.imageshack.us/img98/4770/testwk3.png

So how do I understand such diagram? The upper black dot comprises all the data in all 4 groups or colours, the second highest black dot assumes two groups? But where's the boundary then: between the light blue and green? What are the boundaries of the third black dot? Basically: how do I understand such diagram?

Thanks a lot,
H.

 

[chemisttree]

The Dendogram is meaningless without some context.

(Whew! I'm glad I got through that without cursing...)