206 



BOTANY 



PART 1 



to ascertain which elements are necessary and Avhich superfluous. As 

 Fig. 191, I, shows, the plant (Buckwheat) succeeds Avell in such a 

 food solution if of suitable composition ; it can form roots, shoots, 

 flowers, and fruits, and increase its dry weight a hundred-fold or a 

 thousand-fold, just as if it were gro^Anng in the soil. In distilled 



water on the other hand, while the plant 

 begins to grow normally, the growth 

 soon ceases entirely, and only a very 

 dwarfed plant is produced. The com- 

 position of the food solution (Sachs' 

 solution) is: water, 1000; potassium 

 nitrate, 1 ; calcium sulphate, 0*5 ; mag- 

 nesium suljDhate, 0'5; calcium phosphate, 

 O'o ; iron, a trace. 



From such water-cultures it results 

 that the typical land plant succeeds satis- 

 factorily if supplied with the elements 

 K, Ca, Mg, Fe, and H, 0, S, P, N, if in 

 addition and C (the latter as carbon- 

 dioxide) are available in the atmo- 

 sphere. There are thus in all 10 elements 

 which must be regarded as indispensable 

 food -materials. Of these the seven 

 which remain after excluding H, 0, and 

 C concern us here since the j^lant ob- 

 tains them as nutrient salts from the 

 soil or water. Six of these seven are 

 found in the ash, while the nitrogen 

 escapes on combustion in the form of 

 volatile compounds. That these seven 

 elements are completely indispensable 

 is shown by the fact that if a single 

 one is wanting its loss cannot be made 

 good by an excess of the others, or by 

 the presence of a related element. 



Thus, for example, j^otassium cannot, as 

 a rule, be replaced by sodium, lithium, or 

 rubidium. Lower organisms (Algae, Bacteria, 

 Fungi) are able to do without Ca (-"). The 

 absence of a single necessary element is shown 

 either by the feeble and dwarfed development of the plant (Fig. 191, //, absence 

 of potassium) or by characteristic changes in the plant. The best known of these 

 is the effect of absence of iron, in which case the plant docs not become green 

 (chlorosis) (-'). 



So long as the necessary nutritive substances are provided, the form in which 

 they are ottered to the plants, as well as the proportionate strength of tlie nutrient 

 solution (if not too concentrated), may vary. Plants have the power to take up 



Fig. 191. — Water-cultures of Fagopyrum 

 esculentum. J, In nutrient solution 

 containing potassium ; //, in nutrient 

 solution without potassium. Plants 

 reduced to same scale. (After Xobbe.) 



