ABSORPTION OF ASH-CONSTITUENTS 



83 



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

 for the experiment may be germinated in distilled water. 6 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 solution 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. c 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 



Fig. 49. — Water 

 culture of maize 

 seedling. 



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: Grafe, Viktor, Ernahrungsphysiologisches Praktikum der hoheren 

 Pflanzen. Berlin, 1914, p, 56 el 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. Physiol, res. 1: 327-397. 1915. — Ed. 



b Distilled water is unsuitable for seed germination and for the 

 growth of plants, because (1) it may contain small traces of toxic sub- 

 stances — 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 composi- 

 tion of culture solutions. U. S. Dept. Agric, Bur. Plant Industry. Bull. 231. 1912. True, 

 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. The salt proportions and total concentration of a nutrient solution may be 

 maintained throughout the period of a solution-culture experiment by allowing the solution 

 to flow continuously through the culture jar. (See: Trelease, Sam F., and Livingston, 

 Burton E., Continuous renewal of nutrient solution for plants in water-cultures. Science n.s. 

 55 : 483-486. iQ22.).—Ed. 



