CLOVER CULTURE. 135 



soil ; no nitrogen, no crop; a certain amount yielding practi- 

 cally the same crop, and the crop increasing- with the increase 

 of nitrogen ; but he soon discovered that certain other plants 

 were, under certain circumstances, almost entirely independent 

 of any nitrogen in the soil. He saw to his surprise, as far 

 back as 1862-3, clover and peas growing in a crop of pure 

 sand and producing a full crop of seed, while in other years, 

 and apparently under the same conditions, they starved to 

 death. He discovered that when clover and peas, growing in 

 the most barren soil, had abundance of tubercles they pros- 

 pered, and when the tubercles were wanting, death ensued. 

 He then began a series of most elaborate experiments, con- 

 ducted with the greatest care, to discover under what condi- 

 tions the clovers and other legumes were thus independent of 

 soil nitrogen, and from what source other than the soil they 

 obtained it. It is due to the thoughtful reader that we should 

 detail at some length the nature of these investigations. 



For a soil material to be used in his investigations, Prof. 

 Helriegel selected fine quartz sand, such as is used in the 

 manufacture of glass. This was washed twice and boiled in 

 concentrated muriatic acid three times for the purpose of 

 removing completely every vestige of fertility. As culture 

 vessels, he used cylinders of white glass of different sizes, 

 each having a hole in the bottom for drainage. Pieces of 

 quartz that had been washed carefully and then heated red 

 hot were put in the bottom to afford air drainage. Upon this 

 was placed a thin layer of unsized wadding and on this the 

 sand, which after fertilization in a porcelain vessel was crum- 

 bled into the culture vessels under slight pressure in order to 

 secure the proper degree of porosity and density. The seeds 

 to be used for this purpose were selected with extreme care. 

 From a large number of samples the very heavy and very light 

 were excluded. The remainder were then sprouted between 

 folds of blotting paper, and if there was developed any defect- 

 ive root or abnormal growth it was rejected, the object being 

 to secure even results. Fourteen vessels thus prepared were 

 sown to barley and fertilized with commercial fertilizers, con- 

 taining potash and phosphoric acid, but no nitrogen. Nitro- 

 gen in the form of nitrate of lime was then given in the 

 following proportions: No. 1, .0336 grains ; Nos. 2, 3 and 4, 

 two-thirds of the amount; No. 5, one-half the amount; Nos. 6, 

 7 and 8, one-third of the amount; Nos. 9, 10 and 11, one-sixth 

 of the amount; No. 12, one-twelfth, and Nos. 13 and 14, none. 

 At the end of the first week after sprouting the plants were 

 exactly alike; no difference whatever could be noted. A few 

 days afterward, or as soon as the reserved nutriment in the 



