40 



SOIL CONDITIONS AND PLANT GROWTH 



a larger quantity ; it also affects the straw first. Nitrogen starvation 

 sets in at once, rapidly bringing both grain and straw down to a very 

 low level. 



It is difficult to get behind these effects and ascertain their causes. 

 The function of phosphoric acid in the cell is not easy to discover ; even 

 when the problem is reduced to its simplest state by experimenting 

 with spirogyra in culture solutions little more has been ascertained than 

 that phosphates are wanted for mitotic cell division, doubtless because 

 phosphorus is a constituent of the nucleus, and also for the normal 

 transformations of starch. Loew (i8i) found that fat and albumin 

 accumulated in absence of phosphates, but the colour was yellow and 

 there was no cell division ; as soon as a trace of potassium phosphate 

 was added, however, energetic cell division took place. Reed (236) 

 showed that starch was formed in absence of phosphorus, but did not 

 change to sugars ; erythrodextrin was formed instead and also cellulose. 



The effects of phosphates in raising the quality and feeding value 

 of the crop are very great. The most nutritious pastures in England 

 and the best dairy pastures in France are those richest in phosphates. 

 Paturel ^ has also shown that the best wines contain most PjOj (about 

 0-3 gram per litre), the second and lower qualities containing suc- 

 cessively less. Further, when the vintages for different years were 

 arranged in order of their P^O content a list was obtained almost 

 identical with the order assigned by the wine merchants. 



This close connection between cell division and phosphate supply 

 may account for the large amount of phosphorus compounds stored 

 up in the seed for the use of the young plant, and also the relatively 

 large amounts of phosphate taken from the soil during the early life of 

 the plant. 



Potassium. — Hellriegel has shown (Table XVI.) that equivalent 



Table XVI. — Effect of Potassium Salts on the Growth of Barley. 

 Hellriegel (131). 



' Bull. Soc. Nat. Agric, 1911, p. 977. 



" Lupines, however, could not tolerate the acid condition set up when the mono- 

 phosphate was supplied (p. 138 in (130) ). 



