ii2 BIOLOGICAL PROBLEMS 



fen. No fertilizer overcomes this difficulty. Occa- 

 sionally, in specially favourable seasons, the proper 

 conditions are realized on some of these unsuitable 

 soils: at Rothamsted we had such years for wheat in 

 1863 and 1864, when our crops rose to 56 bushels per 

 acre; and for barley in 1854, 1857, 1861, and 1913, 

 when the yield went to 60 bushels per acre. 



Another phenomenon that may be closely related 

 is tillering-. When the wheat plant germinates it 

 sends up a single shoot. After a time, however, a 

 number of new shoots spring from the base of this 

 shoot, so that there may be ten or a dozen stems from 

 a single seed. This is spoken of as tillering or stool- 

 ing. Tillering is not \vholly, perhaps not even mainly, 

 a question of nutrition, though that is a factor. The 

 unmanured plot on Broadbalk field has received no 

 manure of any sort since 1839; trie plants tiller, but 

 the shoots remain undeveloped, only one or two stems 

 carrying any decent-sized heads. On the adjoining 

 plot, receiving farmyard manure, the tillering is better, 

 and the side shoots all develop. Tillering is improved 

 by constant cultivation : some remarkable wheat plants 

 can be obtained by working under garden conditions. 

 A well-known Eastern method of growing wheat, 

 which is also practised in Russia, consists in periodi- 

 cal hoeing and earthing up of the plants; a great 

 increase in tillering is thus obtained. 



The principle was tested in the eighteenth century 

 by Jethro Tull with remarkable results. During the 

 last few years it has been further developed by Demt- 

 chinsky, 1 whose method was tested both in France 

 and Germany; the yield per plant was greatly in- 

 creased, but, unfortunately, not the yield per unit 



1 See N. and B. Demtchinsky, Mtthode pour obtenir de Forts Rendements 

 en Ctrtales, Paris, 1913; and also A. Einecke, Landw. Jahrb., 1911, 41, 

 281-335, where the method is criticized. 



