328 TEXTBOOK OF BOTANY 



when the supply of some element is inadequate, are referred to as de- 

 ficiency effects, or symptoms, in respect to that element; for example, 

 effects of nitrogen deficiency. The term, of course, refers to the available 

 nitrogen in ammonium or nitrate salts and not to the molecular nitrogen 

 in the air. When a cucumber plant is deficient in nitrogen, the apical 

 end of the fruit is small. When it is deficient in potassium, the basal end 

 of the fruit is small. When plants with thick roots, such as sweet potato, 

 are deficient in potassium or phosphorus, the roots are long and slender 

 because of a failure of cell division in the cambium. Continued cell 

 division in the meristem appears to be related to the fact that mobile 

 ions of potassium and phosphorus accumulate most abundantly in apical 

 meristems. 



Several investigators have made summaries of deficiency symptoms 

 of each of several elements in different species of plants. One of these 

 summaries describing tobacco plants growing in culture solutions is 

 given in abbreviated form below as a basis for comparing symptoms in 

 other kinds of plants. 



Nitrogen deficiency. Plant light green. Lower leaves become yellow, die, 

 and dry to a light-brown color. Stem slender and short. Roots long, with few 

 lateral branches. 



Phosphorus deficiency. Plant dark green. Lower leaves may become yellow, 

 die, and dry to a greenish to black color. Stem slender and short. Roots long, 

 with few lateral branches, reddish brown in color. 



Potassium deficiency. Lower leaves mottled, with dead spots at tips and 

 along margins, which curve downward. Stem slender. Roots long with few 

 branches; yellowish and slimy in appearance. 



Magnesium deficiency. Lower leaves chlorotic (no chlorophyll), usually 

 without spots, and with tips and margins curved upward. Stem slender. Roots 

 long, with few lateral branches; slimy in appearance. 



Iron deficiency. Young leaves chlorotic, usually without spots, principal 

 veins green. Stem slender and short. Root short, with abundant short laterals, 

 brown in color. Terminal bud of stem remains alive. 



Manganese deficiency. Young leaves chlorotic witli scattered dead spots. 

 Leaf appears checkered because of the green color of the small veins. Stem 

 slender. Roots not abundant; brownish in color. Terminal bud of stem re- 

 mains alive. 



Sulfur deficiency. Young leaves light green, no dead spots. Veins lighter 

 green than intervein tissue. Stem short and slender. Roots white, abundant 

 and much branched. Terminal bud of stem remains alive. 



Calcium deficiency. Young leaves in bud curved and hook-like; die at tips 



