Self And The Phenomenon Of Life: A Biologist Examines Life From Molecules To Humanity

The Plant Self 99

“9x6” b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanity

situation stimulates a plant to elongate its stem in order to race to the
top of the canopy.

5.5 Your Roots, My Roots

To the casual eye, roots may look like a tuft of hopelessly entangled wires,
but in fact roots express individuality and have a keen sense of “self” ver-
sus “non-self” discrimination. The most convincing way to demonstrate
this is to grow two plants in a “fence sitting” situation, in which the roots
of each plant straddle two adjacent pots (Fig. 5.2).When compared to a
setup where each plant is grown in its own pot, the sharing plants end
up with a larger root mass and a lower seed mass, indicating increased
root growth at the expense of reproduction, a sign of decreased biolog-
ical fitness. It looks as if each plant is trying to “elbow” away the other

Fig. 5.2. Fence-sitting experiment in beans (Phaseolus varigaris) showing effects of
habitat sharing by two plants. (A) Two plants each with roots equally divided in two
pots (sharing plants). (B) Two plants each with roots in its own pot (owner plants). The
amount of soil and its nutrition content are the same in all the pots. Sixty days later,
fence-sitters show 150% more root mass than those grown in own pots. However, owner
plants show 90% more pod mass, 53% more pods, and 18% more mass per pod, than
fence-sitters. The data show that competition in pot-sharing results in poor health for the
individuals. [See Note 7; permission Springer-Verlag Dordrecht.]