Double fertilization is characteristic feature of angiosperms. Double fertilization was discovered by Nawaschin. It is combination of syngamy i.e., fusion of 'one male gamete with the egg to produce diploid zygote and triple fusion i.e., fusion of diploid secondary nucleus with nucleus of male gamete to produce triploid endosperm.
Emerson found that monochromatic light of more than 680nm shows a sharp reduction in photosynthetic yield. This. phenomenon is known as red drop.