ON THE LIME-FACTOR FOR DIFFERENT CROPS. 383 



plants " ; but it may be objected that such potassa as can be 

 unlocked in the soil by slaked lime or carbonate of lime, can 

 surely also be unlocked by the rootlets themselves. The writer 

 showed years ago that one of the effects of increasing the lime 

 consists in the rich development of rootliairs 1 and this explains 

 satisfactorily the fact that on liming the soil, the plants become 

 capable of absorbing an increased amount of potassa. A second 

 very important physiological effect of lime is the ricli production 

 of dark green and normal chlorophyllbodies. 



The retarding effect of an abnormal excess of lime over 

 magnesia in the soil, or of an excessive liming, may be overcome 

 by an application of powdered magnesite. Burnt magnesia or 

 precipitated carbonate of magnesia should be avoided, being too 

 finely divided and hence much more easily absorbed than the 

 lime compounds. 



It was in the year 1892 that. I first called attention to the 

 importance of a proper ratio between lime and magnesia in the 

 soils, but nobody took notice of my deductions. I had said 2 : 

 " Aus unseren Studien ergibt sich also, dass, em so notwendiger 

 Bestandteil der Pflanzennahrung auch Magnesia salze sind, sic 

 doch bei gewissem Ueberschuss schadlich wirken, wie kein 

 andercs Nahrsalz. 1st zu viel Magnesia im Verhiiltniss zum Kalk 

 vorhanden, so ist eine pathologische Wurzelentwickelung oder 

 baldiger Tod der Wurzeln die Folge , ist aber zu wenig vor- 

 handen, so wird die Entwickelung der Pflanzcn verzogert. Dort 

 treten Gift-, hier Hungersymptome auf. Es ware nun von 

 Interesse, festzustellen, welches Minimum von Magnesia im 

 Koden bei gegebenem Kalkgehalt noch eine annehmbare Ernte 

 zuliisst, und andererseils wie viel Kalk bei gegebener Magnesia 

 menge noting ist, pathologische Erscheinungen zu verhindern." 



It was Mr. May in Washington D.C., who at my suggestion 

 first took this problem up last year and who obtained very 

 decisive results. 3 Among other things he found that in certain 

 cases gypsum can better overcome the injurious action of an 

 excess of magnesia in the soil than carbonate of lime can. 



The writer's theory of the physiological functions of lime 

 and magnesia was first published in Flora (1892) and later on 



1 Flora 1892, p. 384. 



2 Landw. Versuchsstationen, vol. 41, p. 474. 



8 Bulletin No. 1 of the Bureau of Plant Industry, Washington, 1901. 



