It is intended to provide a pure line plant which is required in constructing a seed propagation variety of orchid. An auxin solution is dropped to unfertilized orchid flowers so as to form seeds based on parthenogenesis. Then these seeds are germinated and haploid plants are selected from orchid plants thus grown. The germinating seeds judges as haploid plants are grown to give pure line plants having doubled chromosomes. Thus, a seed propagation variety of orchid is obtained.