Which of the following is best method of germplasm conservation ?

Endangered plants may be preserved in part through seed bank or germplasm bank. The term seed bank sometimes refers to a cryogenic laboratory facility in which the seeds of certain species can be preserved for up to a century or more without losing their fertility. It can also be used to refer to a special type of arboretum where seeds are harvested and the crop is rotated. For plants that cannot be preserved in seed banks, the only other option for preserving germplasm is in vitro storage, where cuttings of plants are kept under strict conditions in glass tubes and vessels.