214 HOW CROPS GROW. 



neous. As Lupke remarks, potassium is rather like nitro- 

 gen, phosphorus, sulphur, etc., one of the elements of 

 which probably a certain quantity is indispensable to the 

 formation of every vegetable cell. Nobbe's results per- 

 haps indicate that buckwheat requires relatively more 

 potassium than the bean for its processes of growth. 

 (Land. MrMcJier, 1888, pp. 887-913.) 



Calcium. Bohm (Jahresbericht tiber Ag. Chemie, 

 1875-6, Bd. I, p. 255) and Von Raumer ( Vs. St., XXIX, 

 251) have furnished evidence that calcium (lime) is di- 

 rectly necessary to the formation of cell-tissue, that is to 

 say, of cellulose. 



This evidence rests upon observations made with seed- 

 lings of the flowering bean (scarlet-runner), Phaseolus 

 multiflorus. When a seed sprouts, the young plant at first 

 is nourished exclusively by the nutritive matters contained 

 in the seed. When its roots enter the soil it begins to de- 

 rive water, nitrogen, and ash-ingredients from the earth. 

 When its leaves unfold in the light it begins to gather 

 carbon from the air and to increase in weight. If its 

 roots are placed in pure water it can acquire no ash-in- 

 gredients ; if its leaves are kept in darkness it can gain 

 nothing from the air. Thus circumstanced, it may live 

 and vegetate for a time, but constantly loses in total dry 

 weight, and its apparent growth is only the formation of 

 new parts at the expense of the old. For some days the 

 young stem shoots upward without green color, but per- 

 fectly formed, and then (in case of the flowering bean) 

 euddenly, at a little space below the terminal bud, a dis- 

 coloration appears, the stem wilts, withers, and dies 

 away. The growth of stem that thus occurs is accom- 

 panied by and depends upon the solution of starch in the 

 seed-lobes and its transfer to the points of growth where 

 it is made over into cellulose the frame-work of the 

 stem. In absence of any external source of ash-ingredi- 

 ents the young stem dies long before the starch of the 



