The main root of Cycas is transient. Abdominal roots are formed after the main root is destroyed. Abdominal roots grow underground. Some parts of the adventitious root emerge above the soil and bifurcate to form branches. Above ground these root bacteria are attacked by Nostoc, Anabaena etc. The normal shape of these affected roots changes and becomes deformed. Because the distorted shape of the root resembles that of sea coral or coral, they are called coralloid roots or coral roots or root tubercles. The part of the cortex of the coralloid root where Nostoc and Anabina reside is called the algal layer.