The Potatoe Plague. 71 



for seed,) has been a potatoe grower for thirty years, used 

 formerly to send five or six hundred bushels of Tawdon kid- 

 neys annually to Selby, where they were used for seed,' and 

 the produce sent to London. He used to grow two hundred 

 bushels to the acre, but now considers fifty bushels a good 

 crop ; has failed so repeatedly the last five years in growing 

 a crop, that this year, 1844, he has none, and believes there 

 is but one man in the township who continues to grow the 

 kidneys. 



I will now state the chemical facts which appear to me to 

 confirm and explain the above-mentioned results of practice. 

 It is notorious to potatoe growers that a marked change takes 

 place in the quality of the tuber when the .stem and leaves 

 wither, and that potatoes taken up when the plant is still 

 growing, are watery, though a portion of the same plot, if of 

 a good sort, and in suitable soil, taken up a few weeks later, 

 will be found light and mealy. This is probably owing to the 

 deposition of starch in the tuber by the descent of the sap, 

 when the growth of the plant has ceased, and is apparently 

 analogous to the very similar process described by Liebig as 

 taking place in all perennial plants. 



" All the carbonic acid which the plants," remarks Liebig, 

 speaking of perennial only, " now absorb, is employed for 

 the production of nutritive matter for the following year. 

 Instead of woody fibre, starch is formed, and is diffused 

 through every part of the plant by the autumnal sap." To 

 remove every doubt on the subject, however, I took up por- 

 tions of two kinds of potatoes, growing in very different situ- 

 ations, and a ripe and unripe sample of each, to an analyzing 

 chemist, merely numbering the samples, and requesting to 

 know the per centage of starch in each. The result was as 

 follows : 



