299 



itself in a scarcity of the reserve substances. Besides this, the lack of 

 potassium explains also the fact, already observed, that shoot formation is 

 retarded, since the cellulose, necessary for the formation of the parenchyma, 

 is likewise a carbo-hydrate. 



Without potassium, the plant becomes green, to be sure, but does not 

 grow much beyond the amount of material furnished from the seed. All 

 other nutritive material, therefore, can not have been used (law of the 

 minimum). According to Nobbe's 

 studies, if the very valuable com- 

 pound, potassium chlorid, was 

 given to potassium hungry plants, 

 even after they had lain dormant 

 for months, an increase in growth 

 was produced in two or th.ree 

 days. The formation of starch 

 began immediately \ An addition 

 of potassium becomes fully effec- 

 tive, however, only when it is not 

 rendered inactive by calcium. Ad. 

 Meyer- emphasizes the especially 

 favorable action of potassium 

 chlorid, but he found this con- 

 siderably weakened when calcium 

 bi-phosphate was also present. 

 With sugar beets potassium 

 chlorid, as well as calcium chlorid, 

 when used alone, worked very 

 well, but not if added simul- 

 taneously. 



Hellriegel found in grain that 

 with a scanty potassium supply, 

 the green parts matured at the 

 expense of the kernels. This is 

 not the case with a lack of nitro- 

 gen ; the plants then develop com- 

 pletely but remain small. In trees 

 a continued lack of potassium 

 always leads to a weaker develop- 

 ment of the end shoots and- finally to "tip blight" and Janson'* states that he 

 has cured this disease by a direct addition of 40 per cent, potassium salt. 

 Naturally tip blight can be produced by ver^^ different causes, and on loamy 

 soils especially other causes must often be sought primarily. 



1 Nobbe, Schroder and Erdmann, Die organische Leistung des Kaliums in der 

 Pflanze. Landwirtsch. Versuchsstat. XIII p. 321. 



2 Jahresber. f. Agrik. Chemie 1880 p. 269. 



3 Janson, A.. Kalidiingung geg-en die Spitzendiirre. Prakt. Ratg-. f. Obst- und 

 Gartenbau 1905 No. 38. 



Fig 



Cross -section through the thorn of 

 Rhamnus cathartica. 



Explanation of letters as in Fig. 37, only here the phello- 

 Ren (d) and secondary bark Ui) are lacking. They appear 

 transformed into permanent cells. (After Dobiier-Nobbe) 



