Viruses completely depend upon host cells for the supply of precursors, energy, enzymes, and the structural machinery — in fact for all the infrastructure except the coded message — for their replication. Viruses are thus parasites at the genetic level. Plant viruses possess no intrinsic mechanism or capacity of their own to push through the cell wall barrier in order to enter the cell. They can come in contact with the cytoplasm or reach the interior of a cell only through wounds caused mechanically or by vectors. Virus particles attach to the cells during mechanical inoculation. Ectodesmata have been suggested as the possible portals of virus entry. Uncoating of virus particles occurs within seconds to minutes after entry of virions into a cell. It is commonly believed that viruses enter the cell as complete virus particles and subsequently disassociate within the interior of the cell.