ABSORPTION OF ASH-CONSTITUENTS 



77 



but the concentration may be raised later to 0.5 per cent." The seed for the 

 experiment may be germinated in distilled water.' As soon as the root has 

 reached a suitable length, the seedling is transferred to the nutrient solution, 

 being fixed in a perforated cork stopper with cotton packing, so that only the 

 root reaches into the solution (Fig. 49) . The culture-bottle should be protected 

 from light, to retard or prevent the development of algae and other organisms, 

 and the vessel is therefore covered with a paper cylinder. Care must be taken 

 that the culture solutipn does not become alkaline during 

 the growth of the plants. To prevent alkalinity a solution 

 of phosphoric acid may be added to the culture solution so 

 as to make it weakly acid." Normal plants, producing 

 flowers and fruit, can be obtained in such water cultures 

 by observing all the necessary precautions. 



Salts that may be used in water-cultures are divided into 

 two groups, those that are physiologically alkaline and 

 those that are physiologically acid. To the first group be- 

 long salts whose anions are absorbed by the plant more 

 rapidly than are their kations, thereby rendering the culture 

 solution alkaline. Potassium nitrate (KNO3) is an example 

 of these. To the second group belong those salts whose 

 kations are absorbed more rapidly than are the anions, 

 thus giving the nutrient medium an acid reaction. Am- 



" This means 0.5 g. of all the salts taken together, dissolved to make 

 100 cc. of solution. — Various other four-salt, and some five-salt, solu- 

 tions have been employed by various workers. For a list of these, 

 see : Graf e, Viktor, Ernahrungsphysiologisches Praktikum der hoheren 

 Pflanzen. Berlin, 1914, p. 56 et seq. The simplest solution yet de- 

 vised for this sort of experiment is that of Shive, which contains 

 but three salts (calcium nitrate, mono-potassium phosphate and 

 magnesium sulphate) besides the iron phosphate. See : Shive, J. W., 

 A three-salt nutrient solution for plants. Amer. jour. bot. 2: 157- 

 160. 1915. Idem, A study of physiological balance in nutrient media. 

 327-397. igis—Ed. 



' Distilled water is unsuitable for seed germination and for the growth of plants, because (i) 

 it may contain small traces of toxic substances — which are more influential in the absence of 

 nutrient salts than in their presence — and (2) it acts to remove salts from the seeds and young 

 seedlings by outward diffusion. See, in this connection: True, R. H., and Bartlett, H. H., 

 Absorption and excretion of salts by roots, as influenced by concentration and composition of 

 culture solutions. U. 'S. Dept. Agric, Bur. Plant Industry. Bull. 231. 1912. Tnie,R.H., 

 Harmful action of distilled water. Amer. jour. bot. 1: 255-273. 1914. Merrill, M. C, 

 Some relations of plants to distilled water and certain dilute toxic solutions. Ann. Missouri 

 Bot. Gard. 2 : 459-506. 1915. Idem, Electrolytic determination of exosmosis from the 

 roots of plants subjected to the action of various agents. Ibid. 2: 507-572. 1915. For 

 earlier work on the physiological properties of distilled water, see: Livingston, B. E., Further 

 studies on the properties of an unproductive soil. U. S. Dept. Agric, Bur. Soils. Bull. 36. 

 1907. It is probably best to allow germination to occur in a properly balanced nutrient 

 solution, frequently renewed. — Ed. 



' Frequent renewal of the solution is necessary in any case, and this avoids any need for 

 adding acid. — Ed. 



Fig. 49. — Water- 

 culture of maize 

 seedling. 



Physiol, res. i : 



