Clear cut difference between General Linear model and Linear mixed model

[Aduragbemi]

I would like to know the clear distinction between a general linear model and linear mixed model. After sourcing for materials i still find it confusing. In addition, i would like to know the requirement for one to use either of the two during analysis. I am planning to work on vernalization and phtoperiod genes and i would have at least three planting date in a year and also repeat this the second year. So i dont still know the clear cut basis for choosing between general linear model and linear mixed model.

[Ksharp]

For General Linear model , the estimate coefficient (beta) is fixed for each variable.

But for Linear mixed model, the estimate coefficient (beta) is different for each variable due to mix effect like : subject, hospital  .