252 WATER-CULTURE. 



675. The constituents may be taken up by the roots in larger 

 proportion than the needs of the plant demand. The excess 

 may (1) remain in solution in the sap of the plant, (2) may es- 

 cape to a slight extent through superficial parts, 1 (3) may form 

 insoluble incrustations or concretions upon or in the plant. 2 



676. The office of the different ash constituents. Potassium. 

 The most conclusive evidence in regard to the importance of this 

 element is afforded by experiments by Nobbe, Schroeder, and 

 Erdmann. 8 Plants of Japanese buckwheat were grown in a 

 nutrient solution free from any trace of a potassium salt. Ex- 

 amination after a few weeks showed that all the organs of the 

 plants were free from starch, and that although the points of 

 growth remained sound, all growth had practically ceased. Even 

 in the chloroplryll-granules not more than a trace of starch could 

 be detected. As soon as a salt of potassium was added to the 

 water, the plants began to grow again, and thenceforth the de- 

 velopment was normal. From the same series of experiments it 

 appeared that the chloride was the best form in which potassium 

 could be given to these plants, and the nitrate the next best ; while 

 on the other hand the phosphate and the sulphate appeared to 

 exert a less favorable effect After use of a solution of the latter 

 salt the leaves were fleshy, more or less rolled up, and it was 

 evident that the starch formed in them was not transferred to 

 the other organs of the plant. Nobbe's statement follows : 

 " The production of starch in the leaves is not dependent upon 

 the form in which potassium is afforded to the plant, but this 



in 100 cubic centimeters of water, to which \ to 3 pro mille of the above salts 

 (see 673) maybe added, and also a trace of ammonic tartrate (Pfeffer, Pflanzen- 

 physiologie, i. p. 254) ; (2) Pasteur (Ann. de Chimie et de Physique, 1862, 

 p. 106) recommends the addition to 100 c.cm. of water, of 10 grams of cane- 

 sugar, .5 gram of ammonic tartrate, and .1 gram of the ash of yeast ; (3) Nageli 

 (Sitzungsb. d. bayer. Akad., 1879) has the following : 100 cm. water, 3 grams 

 cane-sugar, 1 gram ammonic tartrate, 4 grams phosphoric acid neutralized by 

 the ash of peas or wheat ; (4) Nageli suggests also, for the cultivation of 

 Schizomycetes, 100 c.cm. water, .1035 gram hydro-potassic phosphate, .016 

 gram magnesic sulphate, .013 gram potassic sulphate, .0055 gram calcic 

 chloride. 



1 Sachs (Botanische Zeitung, 1862, p. 264) states that drops of water placed 

 on the leaves of Tropseolum and Cucurbita are found after a time to be alkaline. 

 Saussure (Recherches chimiques, 1805, p. 263) asserts that if leaves of fresh 

 plants are washed with water, the ash which they yield on combustion is found 

 to be poorer in alkaline salts than that of leaves which have not been so treated. 



2 Cystoliths and the like, the incrustations upon certain species of Saxi- 

 frage, are cited as examples of the latter. 



Versuchs-Stationen, xiii., 1870, p. 357. 



