100 Self and the Phenomenon of Life
b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanity “9x6”in order to monopolize the territory and the soil nutrients, even to the
detriment of both.^7
A case of kin recognition has been reported for the Great Lakes
beech weed (Cakile edentula), in which allocation to roots increases (a
sign of competition) when groups of “strangers” (from different mater-
nal families) shared a common pot, but not when groups of “siblings”
(kin) shared a pot. As a rule, competition is less intense when the shared
individuals are kin. (“Siblings” are plants grown from seeds coming from
the same mother plant; “strangers” are plants grown from seeds com-
ing from different plants of the same species.)^8 Subsequent reports con-
firmed kin recognition in other plant species.^9
That plants can communicate through roots was elegantly demon-
strated in the following experiment (Fig. 5.3). A pea plant (plant A) is
grown in such a way that half of its roots are in one pot while the other
half are in an adjacent one. The first pot has dry soil whereas the sec-
ond has normal moisture. The second pot is shared with another plant
(plant B), which straddles over another pot that is also shared by plant C.
All the pots except the first have normal moisture. Under this arrange-
ment plant A is drought stressed while plants B and C are not. Plant A
responds by closure of its stomata to conserve water, a normal reaction
Fig. 5.3. Diagram showing the arrangement of pots to demonstrate relay of root stress
cues. Four adjacent pots are positioned in series (from 1 to 4). Pot No. 1 contains soil
that simulates drought conditions; all other pots contain soil with normal moisture. A,
B and C are plants with split roots, each plant straddling two pots. Response to drought
is scored by measuring the closure of stomata (tiny holes on the leaves). All three plants
show positive response even though B and C have no direct contact with the dried soil.
[See Note 10, Falik; permission Elsevier Science.]