132 LECTURE VIII. 



fact is unknown. It will be observed in the table of ash- 

 constituents given above (p. 129) that the greatest increase 

 of phosphorus in the plant takes place during the period 

 of its most active development. Experiments upon animals 

 have shewn that phosphorus and phosphates promote the 

 metabolism of nitrogenous substances, and possibly this may 

 be also the case in plants. As a matter of fact Boussingault 

 and Lawes and Gilbert have found that phosphates exercise 

 an important beneficial influence upon the assimilation of 

 nitrogen, whether supplied in the form of nitrates or of 

 ammonia salts, by the plant. This is clearly shewn by the 

 following table taken from Boussingault. 



The experiments were made with Helianthus-plants. 

 Plant supplied with nitrates and phosphates, 86 days old, contained dry 



solid 21*22 grms : N =0*170 grm. 

 Plant supplied with nitrates, but no phosphates, 72 days old, contained 



dry solid 1*175 grms : N 0*01 6 grm. 

 Plant supplied with ammonium carbonate, but no phosphates, 74 days old, 



contained dry solid 1*130 grms : N = 0*042 grm. 



Potassium. Potassium is absorbed in a variety of com- 

 pounds, such as the sulphate, phosphate, chloride, and pro- 

 bably also the silicate. Of these the chloride is, according 

 to Nobbe, the most advantageous form in which it can be 

 supplied to plants. 



Like phosphorus, potassium is always found in relation 

 with living protoplasm; in fact it appears from de Saussure's 

 observations that the amount of potash in an organ affords an 

 indication of the metabolic activity of the organ. 



This may be illustrated by some analyses, in addition to those given 

 in the above Table (p. 129). 



1. looo parts of Potato-tops contained (Wolff) 



at end of August 2*3 of potash 



at beginning of October ... .. 0*7 



2. The proportion of potash in 100 parts of dry solid of different 

 organs of the Horse-Chestnut (Wolff) : 



Leaves, in the Spring 2*80 



Autumn ... 1*50 



Young wood 0*65 



Bark, young ... 1*60 



