10 Nov., 1917.] Composition of the Potato Plant. 647 



A passing glance at Table V. may create a wrong impression, for it 

 will be at once remarked that, in almost every instance, the old decom- 

 posed sets show a higher analysis of llie essential plant foods than the 

 original set planted, or, rather, the duplicate to the original set planted. 

 The higher percentages in the later harvestings are dne to concentration. 



The analysis of the set at first harvest is really the most valuable 

 analysis, for this set was well preserved, and further than showing a 

 bad colour and a few cracks it was, to all intents and purposes, a sound 

 potato. All the sets obtained during subsequent harvests were eontanii- 

 natcd with sand, and, furthennore, were in an advanced stage of decom- 

 position. In the analyses of the latter the percentages were calculated 

 on the sand-free material. 



The weight of the sets necessarily decreased, but apparently whilst 

 the starch and carbohydrates oxidized, the inorganic constituents and 

 nitrogenous compounds remained ; although towards the final harvest 

 there is a remarkable decrease in the content of potash, this may have 

 been due to leaching. Computing from the analyses (Table V.), we find 

 apparently 50 per cent, of the nitrogen and 25 per cent, of the phos- 

 phoric acid contained in the original potato set has been used in the 

 formation of radical and plumule, root and sprout. The potash appa- 

 rently is not utilized. Probably it i.s stored in the tuber for the good 

 of mankind in supplying a daily medicine. 



The story of seed potato is the direct utilization of the store of 

 nitrogen and phosphoric acid for the formation for the sprout, x^pproxi- 

 mately half the whole amount of the essentials are used up when the old 

 set commences to decay. The starch is slowly oxidized, but the nitrogen 

 and phosphoric acid excess apparently remains in the seed set. Potash 

 plays no part, or, at any rate, is not directly utilized, i.e., does not enter 

 into the new growth, but towards the final stages of decomposition ; a 

 fair amount of this element is dissolved and washed away by soil solution. 



The Composition of the Potato Plant at Various Stages of 



Develop. nent. 



Table I. shows the weights of dry matter found in the root, haulm, 

 and tubers at various stages of growth. At the various harvests portions 

 of the separate parts of the plant were selected and analyzed. 



Similar analyses were conducted by the Ducal Agricultural Experi- 

 ment Station at Bemberg, in Anhalt (Germany), in 1903-4, the experi- 

 menters being the late Professor Dr. H. Wilfarth and Dr. H. Romer. 



Their experiment was on a much larger scale than the one forming 

 the basis of this article. Whilst their results coincide to a degree there 

 are certain marked irregularities in the results obtained by them, which 

 did not show in the experiment reported here. 



Firstly. — It will be observed on reference to the graph on page 648, 

 that a migration of the essential plant foods from the plant to the soil 

 did not take place. This agrees with the finding of the German expert. 



Secondly. — -Whilst the essential plant food percentages generally 

 show higher than the German returns, the most marked is the percent- 

 ages of phosphoric acid. This especially applies to the content in the 

 tubers. 



The high content in phosphoric acid of the tubers obtained in the 

 local experiment in the face of the ordinary percentage occurring in the 

 original seed set requires explanation. The only reason advanced is the 



