EXPERIMENTAL MATERIALS AND METHODS 21 



component assists in the absorption of salt by mycorrhiza, a process 

 which has already been investigated to some extent (Harley and 

 McCready, 1950). 



9. Leaves 



Although terrestrial angiosperms absorb most of their mineral 

 nutrients through the roots, a small amount is taken up via the 

 leaves. The problem of foliar absorption is becoming increasingly 

 important in agriculture and horticulture, and merits more attention 

 from plant physiologists than it has yet received. 



Aquatic angiosperms absorb salts mainly through the leaves, and 

 the mechanism of uptake has been studied in such plants as Elodea 

 (Anacharis) spp., Lemna spp., Potomogeton spp. and Vallisneria spp. 

 Intact plants, segments of shoots bearing leaves, single leaves, and 

 pieces of leaf have been used. Arisz (1953) devised a technique for 

 measuring the rate of longitudinal translocation of chloride ions 

 from one segment of a Vallisneria leaf to another. Transverse 

 movement of calcium ions across leaves has been studied in 

 Potomogeton and other aquatic plants, by using the leaf as a 

 membrane separating two aqueous media (Arens, 1936, Steemann- 

 Nielsen, 1951, Lowenhaupt, 1956). 



10. Cell Organelles 



It is generally assumed that the bulk of the salt absorbed by 

 parenchyma cells is accumulated in vacuoles. In support of this view 

 it has been observed that cells plasmolyzed in hypertonic salt 

 solutions recover at a rate which is consistent with complete transfer 

 of the absorbed ions into the central vacuole (Sutcliffe, 1954a). 

 Isolated vacuoles have been obtained from Allium epidermal cells, 

 and found to behave as osmometers (Chambers and Hofler, 1931; 

 Vreugdenhil, 1957), but their ability to accumulate ions against a 

 concentration gradient has not been demonstrated. 



Intact mitochondria can now be isolated from plant cells, and 

 their metabolic and osmotic properties have been studied in vitro. 

 Following similar work on animal mitochondria, Robertson et at 

 (1955) showed that mitochondria extracted from plants will accum- 

 ulate salts by a mechanism which depends on metabolism. Chloro- 

 plasts and nuclei contain appreciable amounts of inorganic ions, 

 mainly combined with organic substances, but as yet, the mechanism 



M.S.A.P. 



