36i 



the processes taking place. He shows that, exactly as with the use of cal- 

 cium nitrate, potassium nitrate is decomposed by oxalic acid, even in very 

 dilute solutions, in such a way that potassium oxalate and free nitric acid 

 are produced, while oxalic acid does not act strongly on calcium carbonate, 

 since it only coats it with an impervious, thin layer of calcium oxalate. If 

 now the saltpetre in the soil is relatively great in proportion to the acid 

 which a plant species can form, the saltpetre will be taken up, to be sure, 

 but will be decomposed only proportionately to the oxalic acid present, and 

 the free nitric acid is used in the formation of the proteins; the remaining 

 saltpetre is deposited unchanged in. the plant. 



In our cultivated plants the law certainly holds good, that they all re- 

 quire the same nutrients but in different concentrations, and also that their 

 capacity for enduring the accumulation of various substances is decisive 

 for the success of the cultures. It should not be forgotten here, that neither 

 the absolute amount of nutrients, which is borne without any injury, nor 

 also the quantity of any nutrient proved to be the best (optimum) for pro- 

 duction, represents absolutely fixed amounts for any definite plant. Rather, 

 it should be assumed that the need for any definite nutrient changes con- 

 stantly according to the combination in which the other vegetative factors 

 are present at the moment. Thus, there is always a relative optimum and 

 maximum for each vegetative factor. The mode of production and the 

 product, — viz., the plant body, — change according to the momentary com- 

 bination of the vegetative factors ; — thus morphological, anatomical, and 

 chemical analyses give different values for each individual. 



Each change in concentration in the same nutrient mixture changes the 

 method of growth and directly manifests itself, under certain circumstances, 

 in the behavior of the root hairs, as stated by Stieler\ He found in the 

 growing root hair, with each change in the solution, a change (thickening) 

 of the membrane at the end of the root hair; — under certain circumstances, 

 in fact, a cessation of growth occurs. In aqueous solutions of the electro- 

 lytes, the root hairs in many plants form vesicular, irregular widenings, and 

 can even crack open at the tip or (rarely) laterally. The non-electrolytes 

 exercise an injurious influence, only if they have a poisonous effect or are 

 present in too high a concentration, which causes plasmolysis. The ob- 

 servation that concentrated magnesium compounds can be proved to act 

 directly poisonously, is especially noteworthy. This cannot be observed 

 for other nutritive salts even with high concentration. 



These investigations confirm my own observations, viz., that, in a 

 highly concentrated nutrient solution, "gnarled or distended" root hairs 

 appear, and thereby indicate that the plant has had to combat difficulties in 

 absorbing its food. 



In regard to varieties of grain, the experiments indicate that oats, for 

 example, can suffer from the amounts of nutrients wdiich, for wheat, make 



1 Stieler, G., tJber das Verhalten der Wurzelharchen gegen Losungen, Disser- 

 tation. Kiel 1903. Cit. Bot. Centralbl. v. Lotsy 1904, No. 47, p. 541. 



