18 MINERAL SALTS ABSORPTION IN PLANTS 



factors in coconut milk (Steward and Shantz, 1956) has placed a new 

 and valuable experimental material in the hands of plant 

 physiologists. The tissue cultures, as grown at present, are not 

 entirely satisfactory for investigations of salt absorption, because 

 the gradual isolation of innermost cells from the medium as growth 

 proceeds results in extensive differentiation. To avoid such 

 difficulties attempts are being made to produce dispersed cultures of 

 meristematic cells, preferably with synchronized divisions, which 

 can be stimulated at will to pass into the vacuolated condition. 



5. Micro-organisms 



Unicellular algae, yeasts and bacteria can be grown relatively 

 easily in pure culture under controlled conditions, and have been 

 used extensively in the study of salt absorption. Investigations with 

 these organisms might contribute greatly to a unified theory of salt 

 accumulation in plants, if microbiologists and plant physiologists 

 had greater liaison. 



Advantages exhibited by micro-organisms over cells of higher 

 plants for physiological investigations include : 



(a) the more rapid rates of metabolism and growth; 



(b) the relative ease with which cell division and enlargement can 

 be distinguished in the growth of a population ; and 



(c) the wide range of conditions, e.g. of aeration and nutrient 

 supply, under which growth occurs. 



Micro-organisms have a less extensive vacuole system than is 

 found in parenchyma cells of higher plants (Fig. 5), and one may 

 therefore predict the existence of interesting differences between 

 absorption mechanisms in the various cell types. Meristematic cells 

 of higher plants may have more in common with micro-organisms 

 than with parenchyma in this respect. 



6. Multicellular Algae 



The ability of multicellular algae to survive in sea-water has 

 received considerable attention, as will be described in Chapter 9, 

 and such studies may assist in solving some of the more general 

 problems of salt absorption. Investigations have mainly been 

 confined to species, such as Ulva lactuca and Porphyra perforata, 

 which have thin flattened fronds, consisting of two layers of rather 



