Comparative anatomy of the adventitious roots of Poa annua and Poa pratensis
The adventitious roots of Poa annua and Poa pratensis are described both externally and internally. The roots of the two species differ in the size, length, position, and amount of xylem. The adventitous roots of Poa annua resemble the lateral roots of Poa pratensis, with the exception of the central duct which is made by the breakdown of the walls between two contiguous late metaxylem vessels in P. pratensis and P. annua, it is a single late metaxylem vessel. The adventitious roots of Poa annua produce more root hairs than do the laterals or sub-laterals, but Poa prantensis the lateral roots give rise to branches, but the sub-laterals apparently never branch. Poa prantensis exhibits two to four times as much branching as does Poa annua.