522 OCCASIONAL FAILURE OF SEED POTATOES. 



tures of the nitrate of soda with the sulphate of soda or with the sulphate 

 of magnesia.* The effect of such mixtures affords a beautiful illustration 

 of the principle I have frequently before had occasion to press upon your 

 attention — that plants require for their healthy growth a constant supply 

 of a considerable number of different organic and inorganic substances. 

 Thus upon a field of potatoes, the whole of which was manured alike 

 with 40 cart loads of dung, the addition of— ^ 



a. Nitrate of soda alone gave an increase of 3|^ tons. 



Sulphate of soda alone gave ... '* ' 



While one half of each gave 



h. Sulphate of ammonia. alone gave 



Sulphate of soda 



But one half of each gave . . 





c. Nitrate of soda alone gave . . 

 Sulphate of magnesia alone gave 

 And one half of each gave . . 



These results are very interesting, and when confirmed by future re- 

 petitions of such experiments — and followed up by an examination of 

 the quality and composition of the several samples of potatoes produced — 

 cannot fail to lead to very important practical conclusions- 



7°. Occasional failure of seed potatoes. — The seeds of all cultivated 

 plants are known at times to fail, and the necessity of an occasional 

 change of seed is recognised in almost every district. In the Lowlands 

 of Scotland potatoes brought from the Highlands are generally pre- 

 ferred for seed, and on the banks of the Tyne Scottish potatoes bring a 

 higher price for seed than those of native growth. This superior quality 

 is supposed by some to arise from the less perfect ripening of the upland 

 potatoes, and in conformity with this view the extensive failures which 

 have taken place during the present summer (1643) have been ascribeo 

 to the unusual degree of ripeness attained by the potatoes during the 

 warm dry autumn of the past year. 



This may in part be a true explanation of the fact, if — as is said — the 

 ripest potatoes always contain the largest proportion of starch — since 

 some very interesting observations of Mr. Stirrat, of Paisley, would 

 seem to indicate that whatever increases the per-centage of starch, in- 

 creases also the risk of failure in potatoes that are to be used for seed.f 

 This subject is highly deserving of further investigation. 



' For the particulars of these experiments see the Appendix. 



t I insert Mr. Stirrat's letter upon this subject, not only because his observations are in- 

 teresting in themselves, but because they are really deserving of the careful attention 'of 

 practical men : — 



"Sir,— The following experiment with potatoes was tried with the view of discovering the 

 cause of so many failures in the crops of late years, from the seed not vegetating, and rotting 

 in the ground. I had an idea that the vegetative principle of the plant might become weak 

 In consequence of being grown on land that had been a long time subjected to cropping, and 

 not allowed any length of lime to lie at rest. I, therefore, raised a few bolls on land that liad 

 Iain lea for 70 years (being part of my bleach green), and found that these on being planted 

 Bgain the following year were remarlcably strong and healthy, and not a plant gave way, and 

 I have continued the same method for the last six years, and the result has, in every instance, 

 been equally favourable. Four years ago, one boll of my seed potatoes was planted along 

 with some others in a field of about an acre, the other seed was grown on the farm, and the 

 •eed all gave way ezceptiog that got from me. They were all planted at the same time and 



