Mistletoe is a parasitic plant that grows on different host trees. It is often found on trees that are diseased. Much like cancer can only grow on a human or an animal when something is a bit out of balance, mistletoe is parasitic in nature. Host trees can be manifold. Birds propagate the mistletoe seeds from the berries though their droppings into other trees after they consumed them. This gives the seeds and extra protection to catching on to the host tree and start growing. They find their soil in symbiosis with the tree and use the nutrients from the tree to grow and propagate. Much like cancer uses the nutrients from he human or animal environment to grow. The mistletoe plant is typically round like the microscopic cell. One can often see lots or even hundreds of mistletoe plants along a row of trees at the side of a river, displaying there roundness like a cabbage head in the trees against the horizon, especially when the foliage of the tree might be gone in autumn and winter.
Depending on where you are and life forces of the area and climate and species, in Europe for instance, a little growth of a mistletoe plant might be as little as an inch or so a year for extending its circular growth at the periphery. Other areas it might grow faster. Some mistletoe species in certain areas are used for medical purposes, especially treatments for certain cancers. In Europe, this has been used for about a hundred years and has made it into mainstream medicine.