V. NEW APPROACH TO WATER RELATIONS OF DESERT PLANTS
285
series (Walter, 1936, p. 186). The objection of van Eijk (1939, p. 587)
against the importance of the lyotropic series is based on the absence of
succulence when Cl~ in the nutrient solution is replaced by N0 3 ", while
nitrate is even more effective than Cl~ in the lyotropic series. However, van
Eijk did not determine the actual concentration of the cell sap and did not
account for the metabolic utilization of the nitrate ion.
It should be emphasized that the chloride content of the soil is of little
importance for estimating the chloride present in the leaf since the different
plant species and varieties absorb chloride ions to different degrees. Also
the chloride content of the leaf ash gives no indication of chloride concentration inside leaf cells.
Aside from the usual uptake through roots, plants growing on the seashore are able to take up chloride through leaves when moistened by seawater spray. Leaves exposed to the wind have a Cl~ content about three-six
times higher than leaves on the lee side (Boyce, 1954, p. 54). The succulence observed in these experiments resulted from an increase in size of
the chlorophyll-free mesophyll cells and was especially pronounced in salttolerant species. Here, too, development of succulence was found to be
a specific effect of the chloride ion independent of the cation applied. Sulfate ions do not cause such succulence.
XX. Chloride Accumulation in Halophytes
Since there are no basic differences between halophytes of arid lands
and of the seashore, the latter will also be included in this discussion. Most
experiments of salt effects were performed with more or less salt-tolerant
species or varieties of economically important agricultural plants, although
these plants are glycophytes and therefore grow best on salt-free soils. In
contrast, true halophytes grow better in soils with limited salt content.
When these plants are cultivated in salt-free soil, they take up traces of
chlorides, which are found in every soil, and accumulate them in leaves,
so that the chloride content of the leaf cell sap is relatively high (see p.
287).* Also in natural habitat the chloride uptake is relatively higher at
low soil chloride content than at high salt content (Önal, 1966, pp.
225-226). However, with increasing soil salt concentration, most halophytic plants take up only enough salt to compensate the osmotic potential
of the soil solution.
* Such chloride accumulation may be found already in varieties close to halophytes
as in the sugar beet (Beta vulgaris spp. vulgaris var. altissima), which developed
from the coastal Beta vulgaris spp. maritima. Leaves of the sugar beet have an ash
content of about 15.5% chlorides (Trifolium pratense has only 3.8%).
285
series (Walter, 1936, p. 186). The objection of van Eijk (1939, p. 587)
against the importance of the lyotropic series is based on the absence of
succulence when Cl~ in the nutrient solution is replaced by N0 3 ", while
nitrate is even more effective than Cl~ in the lyotropic series. However, van
Eijk did not determine the actual concentration of the cell sap and did not
account for the metabolic utilization of the nitrate ion.
It should be emphasized that the chloride content of the soil is of little
importance for estimating the chloride present in the leaf since the different
plant species and varieties absorb chloride ions to different degrees. Also
the chloride content of the leaf ash gives no indication of chloride concentration inside leaf cells.
Aside from the usual uptake through roots, plants growing on the seashore are able to take up chloride through leaves when moistened by seawater spray. Leaves exposed to the wind have a Cl~ content about three-six
times higher than leaves on the lee side (Boyce, 1954, p. 54). The succulence observed in these experiments resulted from an increase in size of
the chlorophyll-free mesophyll cells and was especially pronounced in salttolerant species. Here, too, development of succulence was found to be
a specific effect of the chloride ion independent of the cation applied. Sulfate ions do not cause such succulence.
XX. Chloride Accumulation in Halophytes
Since there are no basic differences between halophytes of arid lands
and of the seashore, the latter will also be included in this discussion. Most
experiments of salt effects were performed with more or less salt-tolerant
species or varieties of economically important agricultural plants, although
these plants are glycophytes and therefore grow best on salt-free soils. In
contrast, true halophytes grow better in soils with limited salt content.
When these plants are cultivated in salt-free soil, they take up traces of
chlorides, which are found in every soil, and accumulate them in leaves,
so that the chloride content of the leaf cell sap is relatively high (see p.
287).* Also in natural habitat the chloride uptake is relatively higher at
low soil chloride content than at high salt content (Önal, 1966, pp.
225-226). However, with increasing soil salt concentration, most halophytic plants take up only enough salt to compensate the osmotic potential
of the soil solution.
* Such chloride accumulation may be found already in varieties close to halophytes
as in the sugar beet (Beta vulgaris spp. vulgaris var. altissima), which developed
from the coastal Beta vulgaris spp. maritima. Leaves of the sugar beet have an ash
content of about 15.5% chlorides (Trifolium pratense has only 3.8%).