Priinns spinosa, etc., are \txy 

 apt to injure people working 

 among them. The transfor- 

 mation of the thorns into nor- 

 mal leafy shoots, ending with 

 a terminal bud, results from 

 |)runing and transplanting the 

 wild plants to rich, loose, well 

 drained soils. 



c. Changes in Production 

 due to a lack of 



Potassium. 

 By way of introduction, 

 reference must be made once 

 more to the fact that a lack 

 of potassium in the soil condi- 

 tions a lack of moisture. Holl- 

 rung's^ recent experiments 

 have proved that a soil mixed 

 with potassium salts contains 

 much more moisture than the 

 same soil under otherwise 

 similar conditions. 



The potassium enters the 

 plant in the form of potassium 

 nitrate, sulfate and phosphate, 

 chlorid or even silicate. In 

 the plant it may be found in 

 combination with organic and 

 inorganic salts and especially 

 in the tissues in which carbo- 

 hydrates may be found. Hell- 

 ricgel andW'ilfarth proved ex- 

 perimentally that the amount 

 of carbo-hydrates deposited 

 as reserve substances (starch 

 and sugar) in potatoes, grain 

 and sugar beets, depends 

 directly on the amount of 

 potassium supplied. Thus 

 it is evident that a lack 

 of potassium must manifest 



Fig. 37. Cross-section through a one-year old 

 branch of Rhamnus cathartica. 



1 Hollrung-, Vortrag- im An- 

 haltinischen Zweigverein fiir 

 Zuckerriibenkultur. Blatter f. 

 Zuckerriibenbau 1905 p. 76. 



a Cuticiila, h Epidermis, c Cork layer, li 

 I'lielloKen (cork cambium), e CoUen- 

 chyma./and/' Bark parenchyma, 5" and.tr' 

 Bast bundles. /; Secondary bark. / Wood, 

 and on its i)erii)lierv. the cambial zone, 

 k Pitli, III pith disc, (.\fter I)obner-NobV)e) 



