Types of Roots

Initially undifferentiated root cells grow downwards to establish a base of primary growth. This growth is the result of the apical meristem and is primarily for elongation. Secondary growth involves cellular growth outward (i.e. thickening the root). These thickened roots can become incredibly robust, underground branches. Annual secondary growth produces secondary xylem which although is dead, conducts water and provides strength. For the purposes of our experiment both their inflexibility and the slow growth of these roots deems them unsuitable.
So, we can’t use trees. Thankfully there are smaller vascular plants that grow faster and don’t need to invest time and resources in extensive, robust root systems to anchor large plant bodies. These shall be the plants for us. Fast growing smaller plants require fast growing roots and fast growing roots grow downward primary roots and then secondary lateral roots that increase surface area and anchorage. It is this branching mass of roots that would seem most suitable for our project.

Raven, JA & D Edwards. 2001. Roots: evolutionary origins and biogeochemical significance. J. Exp. Bot. 52, Roots Special Issue: 381-401
Sutton, RF & RW Tinus. 1983. Root and root system terminology. Forest Science Monograph 24 : 137.