10 Nov.. 1917.] Composition of the Potato Plant. 



653 



entered the i)hiui ^luring the first month's growth. Diiriiii; the second 

 month approxiinateli/ four-fifths of fho total requirement of phosphoric 

 acid and nitrogen had been acquired, whilst of the total requirement 

 as regards the bases {potash, lime, and magnesia) from one-half to two- 

 thirds had been acquired at the end of the second month. Practically 

 the whole requirement of nitrogen, potash, and magnesia has entered 

 the plant by the end of the third month, but the figures show that 

 approximately 10 per cent, of the total requirement in phosphoric acid 

 and lime enters the plant after the tliird month. 



Rate of Growth of the Plant. 



Computing from Table II. on page 644, it is found that the potato 

 plant produces 9 per cent, of the total dry matter during the first month's 

 growth. This increases to approximately 50 per cent, during the second 

 month, and further increases during the third month to 91 per cent, of 

 the total dnj matter i^roduced. Th\i.s. we have the three cycles in the life 

 of the potato plant. The first is preparation, and it is here that the plant 

 asks for assistance. The second is production. The third is maturation. 



Soluble Plant Foods in the Haulm of the Potato Plant at 

 Various Stages of Growth. 



The analyses were conducted on the absolutely dry material, the 

 method being to mix 3 grams of the dry pulverized haulm with 300 ecs. 

 of distilled water. The vessel containing the mixture was allowed to 

 remain at a temperature of 17 deg. C. for 17 hours. 



The extract was then filtered off and the residue washed with 100 ces. 

 cold distilled aqua. 



The filtrate was evaporated to 300 ces. and an aliquot taken for the 

 estimation of nitrogen, potash, and phosjjhoric acid. The usual official 

 method being used in each case. 



The results are given in the following table : — 



Table XIII. 

 SoLrBLE Plaxt Food in the Potato Haulm at Various Stages of 



Development. 



These figures are interesting in that they show the greatest solubility 

 in the case of potash. The phosphoric acid is apparently mostly 

 soluble, but the greater part of the nitrogen is obviously held in insoluble 

 organic combination. It will be noticed that although the percentages 

 on the dry material show a pronounced decrease in each successive har- 

 vest, this decrease is directly proportional to the total amount of plant 

 food present. Therefore the percentage of water-soluble plant food, 

 calculated on the total present, remains fairly constant. 



