Water and Solute Permeability of Plant Cuticles: Measurement and ...

5.2 Experimental Methods 129
Fig. 5.2 Bright field micrographs of leaf surfaces of Phaseolus vulgaris after treatment with silver
nitrate (AgNO 3 ) solution for 1 h. Sites of a strong silver precipitation are anticlinal cell walls,
cuticular ledges and glandular trichomes. Data from Schönherr (1969)
Fig. 5.3 Surface view of mercury precipitates in Allium (a) and Convallaria (b) leaf epidermal
walls. (Taken from Schönherr and Bukovac 1970a)
Copious amounts of mercury precipitates can be found in anticlinal walls, while
over periclinal walls mercury is rarely found. The effect of removing waxes on
distribution pattern indicates that waxy domains are impermeable to HgCl 2 , even
though it dissolves in benzene. Perhaps crystalline wax domains are impermeable
to HgCl 2 , while amorphous waxes are not. This would imply that precipitates form
in the cell wall wherever the cuticle is free of crystalline waxes. This apparently
applies also to silver precipitates and distribution of berberine chloride (Figs. 5.1
and 5.2).
5.2 Experimental Methods
Permeability of cuticles to polar non-electrolytes (Sect. 6.2; Fig. 6.23) and electrolytes
is very low and difficult to measure accurately. Quantitative measurements
require maximum driving force—that is, concentrated solutions. This can