Subject: Why are salt crystals forming on the outside of a glass instead on a string

I am doing a science experiment that I got out of a book.  The experiment was 
to grow "stalagtites and stalagmites" on a string by using Espson salts.  I 
followed the instructions: filling 4 glasses with water and salt solution, then 
placing a black yarn from one glass to another making an X.  The crystals were 
supposed to form on the string making a "stalagtite" and then dripping onto the 
surface making a "stalagmite".  The problem is that the crystals never formed 
on the string, but started forming in clusters on the outsides of the glasses.  
I did the experiement twice with the same results.  Why would the crystals form 
on the outside of the glasses instead of the yarn?

Re: Why are salt crystals forming on the outside of a glass instead on a string