Low phosphorus or iron causes the proteoid type of this structure, which forms clusters.   
Low phosphorus or iron causes the proteoid type of this structure, which forms clusters.   The radicle is the embryonic form of this structure, and this structure's caps contain the  growing tips. One type of this structure is the (*) "tap" variety, and nitrogen fixation occurs in its  nodules. Edible types of this structure include beets and carrots. For 10 points, name this structure  that takes in water and nutrients and keeps plants fixed to the ground.
Low phosphorus or iron causes the proteoid type of this structure, which forms clusters.   
roots