156 PHARMACEUTICAL BOTANY 
growth is retarded. Without sufficient sulfur, cell-division and 
fruit formation are checked. Deficiency in phosphorus retards 
the maturation of the plant. 
Fic. 93.—Median longitudinal section through the root tip of the barley. f, 
calyptrogen; d, dermatogen, c, the thick outer wall of the same; pr, periblem; fl, 
plerome; en, endodermis; /, intercellular-air-spaces; a, cell rows which will develop 
the central vessels; 7, detached cells of root cap; s, starch grains in cells of root 
cap. X 180. (After Strasburger and Koernicke in Lehrbuch der Botanik.) 
Calcium not only neutralizes many harmful substances but 
facilitates the absorption of other salts and is necessary for normal 
leaf development. It is the chief element in the ash of leaves. 
Potassium accompanies carbohydrates during their transloca- 
tion and is thought to play a part in their formation. 
