But some interesting facts or clues are known. Cytokinens are found at a higher than normal level in a witches'-broom. Cytokinens are hormones that do not move very freely around the plant. Their presence stimulates cell divisions. The hormone, giberillen, which encourages shoot elongation is present at reduced levels, especially in a virally produced broom.
Picture above shows a broom on Abies concolor that has been difficult to propagate.
How these unknown agents upset the hormonal balances in a bud and how they are able to persist into the resulting brooms are questions that still need explanation. Since these agents apparently have a genetic influence as well, the questions are even more complex than they first appear. Grafting a small piece of a 'nonviral' witches'-broom onto a seedling will generally create a plant with the characteristics of the original broom. The hormonal imbalance apparently remains, even though a new stem and root system have been added. Either a causative agent was in the piece of broom that was grafted or the genetic structure of the cells was imprinted with a new hormonal code equal to that of the whole broom.