The anatomy of roots and mycorrhizae of the orchidDendrobium cunninghamii Lindl

Abstract

The root cap develops out of the cells of the caliptrodermatogen. The root apex belongs to the first of Haberlandt’s histogen types. The velamen usually consists of three layers of cells, and develops out of the protoderm by periclinal divisions. Funnel-shaped cells later divide tangentially into two cells, and in one of these cells a fibrous body develops. Two to four thick-walled cells alternate, usually with one passage cell in the exodermis. The cortex proper consists of approximately ten to twelve layers of parenchymatic cells in the mature root. There are eight to sixteen xylem poles alternating with the same number of phloem poles in the central cylinder. In the roots ofDendrobium cunninghamii I observed two types of mycorrhizal infection, which can be classified as transitive types between ptyophagus and tolypophagus mycorrhizae. In my opinion, a state of balanced symbiosis exists between the fungus and the plant; a part of the time the plant acts as a parasite on the fungus.