My book says that
Glucose is found to exist in two different crystalline forms which are named as $\alpha$ and $\beta$.
Next it says that
This behaviour could not be explained by the open chain structure for glucose.
I am not able figure out how does existence of two crystalline forms prove that glucose exists as a cyclic structure? Are there no noncyclic compounds which exist in more than once crystalline forms?
And why can't it be explained by the open chain structure?
I think I am missing something, but what?
If we take the example of glycine, it exists in two different crystalline forms, but doesn't have a cyclic structure like that of glucose. So why does existence of two crystalline forms for glucose seen as a supporting evidence of its ring form?