Endosperm with Chalazal Haustorium

In Grevillea robusta, a member of Proteaceae the endosperm is of the free nuclear type. The upper part of endosperm becomes cellular, whereas the lower part develops into a coenocytic, coiled worm-like structure called the 'vermiform appendage'. It serves as an aggressive haustorium, invades the chalaza1 tissue and transports nutrients to the main endosperm. The occurrence of a chalazal haustorium is also reported in several other plants viz. Macadamia thymifolia, Magnolia obovata, Iodinia rhombifolia etc.

The longest endosperm haustorium is found in Echinocystis lobata of the family, Cucurbitaceae. In Lomalia, besides the chalazal haustorium, numerous single-celled, finger-like projections arise from the cellular endosperm. These penetrate the nutritive nucellar tissue and help in increasing the absorptive surface of the endosperm.