V. NEW APPROACH TO WATER RELATIONS OF DESERT PLANTS
251
lOOx
50
50 h
Osmotic potential (atm)
20
- 3 0
100
L
Fig. 19. Relation between osmotic potential (hydrature) and root and shoot
growth of Pisum sativum seedlings (after Walter, 1924, p. 409, Fig. 10, 1962,
p. 345. Fig. 231).
from plants of the first three vessels only. The osmotic potential decreased
from —3 atm (vessel A) to —11 atm for vessel C (see Fig. 20).
In a similar experiment the soil was moistened uniformly throughout
the vessels to A, 15.5%; B, 6.7%; C, 4 . 3 % ; D, 2.5%; E, 1.3%. The
presoaked Brassica seeds were put on the soil surface and the root and
shoot length of the seedlings measured after 5 days. The height of the
above-ground parts of the plants decreased from 19 mm (A) to 7 mm ( E ) .
Although the length of the main root increased from 21 mm (A) to 38 mm
(E), the root was less branched and thinner. At high soil moisture contents,
the main root was shorter than at low moisture content but formed numerous lateral roots (Fig. 21).
The relation between osmotic potential ψ 8 , root and shoot growth, and
the importance of ψ 8 as an ecophysiological indicator was also shown in