Tertiary roots are 

A. Positively geotropic 

B. Negatively geotropic 

C. Plagiogeotropic 

D. Ageotropic

In a mature root system, secondary and tertiary roots form lateral branches < 0.6 mm in diameter and serve distinct functions. Lateral roots arise horizontally from the primary (tap) root, anchoring the plant and enhancing water and nutrient uptake. Tertiary roots are branches of secondary roots. Some lateral organs show little or no response to gravity (ageotropic), e.g., the coralloid roots of Cycas.

Taproot:

The taproot is the primary root derived from the embryo’s radicle and usually persists for the plant’s life, giving rise to secondary (lateral) roots, which further branch into tertiary roots. 

Hence, the correct answer is option D.