The quality of preservation in coal balls varies from no preservation to the point of being able to analyse the cellular structures.[9] Some coal balls contain preserved root hairs,[31] pollen,[32] and spores,[32] and are described as being "more or less perfectly preserved",[33] containing "not what used to be the plant", but rather, the plant itself.[34] Others have been found to be "botanically worthless",[35] with the organic matter having deteriorated before becoming a coal ball.[36] Coal balls with well-preserved contents are useful to paleobotanists.[37] They have been used to analyse the geographical distribution of vegetation: for example, providing evidence that Ukrainian and Oklahoman plants of the tropical belt were once the same.[38] Research on coal balls has also led to the discovery of more than 130 genera and 350 species.[1]